ISIS leader purportedly accepts Boko Haram’s pledge of allegiance

By Hamdi Alkhshali and Steve Almasy, CNN
Updated 8:11 PM EDT, Thu March 12, 2015
A video of Abubakar Shekau, who claims to be the leader of the Nigerian Islamist extremist group Boko Haram, is shown in September 2013. Boko Haram is an Islamist militant group waging a campaign of violence in northern Nigeria. The group
Photos: Boko Haram: Nigeria's crisis
A video of Abubakar Shekau, who claims to be the leader of the Nigerian Islamist extremist group Boko Haram, is shown in September 2013. Boko Haram is an Islamist militant group waging a campaign of violence in northern Nigeria. The group's ambitions range from the stricter enforcement of Sharia law to the total destruction of the Nigerian state and its government. Click through to see recent bloody incidents in this strife-torn West African nation:
PHOTO: Boko Haram/Getty Images
Photos: Syria's civil war, in pictures
Bodies lie in the streets in Maiduguri, Nigeria, after religious clashes on July 31, 2009. Boko Haram exploded onto the national scene in 2009 when 700 people were killed in widespread clashes across the north between the group and the Nigerian military.
Photos: Boko Haram: Nigeria's crisis
Bodies lie in the streets in Maiduguri, Nigeria, after religious clashes on July 31, 2009. Boko Haram exploded onto the national scene in 2009 when 700 people were killed in widespread clashes across the north between the group and the Nigerian military.
PHOTO: Aminuo Abubacar/REUTERS/Landov
An official displays burned equipment inside a prison in Bauchi, Nigeria, on September 9, 2010, after the prison was attacked by suspected members of Boko Haram two days earlier. About 720 inmates escaped during the prison break, and police suspect the prison was attacked because it was holding 80 members of the sect.
Photos: Boko Haram: Nigeria's crisis
An official displays burned equipment inside a prison in Bauchi, Nigeria, on September 9, 2010, after the prison was attacked by suspected members of Boko Haram two days earlier. About 720 inmates escaped during the prison break, and police suspect the prison was attacked because it was holding 80 members of the sect.
PHOTO: Sunday Alamba/AP
Nigerian President Goodluck Jonathan, second from left, stands on the back of a vehicle after being sworn-in as President during a ceremony in the capital of Abuja on May 29, 2011. In December 2011, Jonathan declared a state of emergency in parts of the country afflicted by violence from Boko Haram.
Photos: Boko Haram: Nigeria's crisis
Nigerian President Goodluck Jonathan, second from left, stands on the back of a vehicle after being sworn-in as President during a ceremony in the capital of Abuja on May 29, 2011. In December 2011, Jonathan declared a state of emergency in parts of the country afflicted by violence from Boko Haram.
PHOTO: STRINGER/EPA/LANDOV
Rescue workers help a wounded person from a U.N. building in Abuja, Nigeria, on August 26, 2011. The building was rocked by a bomb that killed at least 23 people, leaving others trapped and causing heavy damage. Boko Haram had claimed responsibility for the attack in which a Honda packed with explosives rammed into the U.N. building, shattering windows and setting the place afire.
Photos: Boko Haram: Nigeria's crisis
Rescue workers help a wounded person from a U.N. building in Abuja, Nigeria, on August 26, 2011. The building was rocked by a bomb that killed at least 23 people, leaving others trapped and causing heavy damage. Boko Haram had claimed responsibility for the attack in which a Honda packed with explosives rammed into the U.N. building, shattering windows and setting the place afire.
PHOTO: Henry Chukwuedo/AFP/Getty Images
A photo taken on November 6, 2011, shows state police headquarters burned by a series of attacks that targeted police stations, mosques and churches in Damaturu, Nigeria, on November 4, 2011. Attackers left scores injured -- probably more than 100 -- in a three-hour rampage, and 63 people died.
Photos: Boko Haram: Nigeria's crisis
A photo taken on November 6, 2011, shows state police headquarters burned by a series of attacks that targeted police stations, mosques and churches in Damaturu, Nigeria, on November 4, 2011. Attackers left scores injured -- probably more than 100 -- in a three-hour rampage, and 63 people died.
PHOTO: AMINU ABUBAKAR/AFP/Getty Images
Men look at the wreckage of a car after a bomb blast at St. Theresa Catholic Church outside Abuja on December 25, 2011. A string of bombs struck churches in five Nigerian cities, leaving dozens dead and wounded on the Christmas holiday, authorities and witnesses said. Boko Haram
Photos: Boko Haram: Nigeria's crisis
Men look at the wreckage of a car after a bomb blast at St. Theresa Catholic Church outside Abuja on December 25, 2011. A string of bombs struck churches in five Nigerian cities, leaving dozens dead and wounded on the Christmas holiday, authorities and witnesses said. Boko Haram's targets included police outposts and churches as well as places associated with "Western influence."
PHOTO: Sunday Aghaeze/AFP/Getty Images
A paramedic helps a young man as he leaves a hospital in the northern Nigerian city of Kano on January 21, 2012. A spate of bombings and shootings left more than 200 people dead in Nigeria
Photos: Boko Haram: Nigeria's crisis
A paramedic helps a young man as he leaves a hospital in the northern Nigerian city of Kano on January 21, 2012. A spate of bombings and shootings left more than 200 people dead in Nigeria's second-largest city. Three days later, a joint military task force in Nigeria arrested 158 suspected members of Boko Haram.
PHOTO: AMINU ABUBAKAR/AFP/Getty Images
A photo taken on June 18, 2012, shows a car vandalized after three church bombings and retaliatory attacks in northern Nigeria killed at least 50 people and injured more than 130 others, the Nigerian Red Cross Society said.
Photos: Boko Haram: Nigeria's crisis
A photo taken on June 18, 2012, shows a car vandalized after three church bombings and retaliatory attacks in northern Nigeria killed at least 50 people and injured more than 130 others, the Nigerian Red Cross Society said.
PHOTO: Victor Ulasi/AFP/Getty Images
A French family kidnapped February 19, 2013, in northern Cameroon is released after two months in captivity in Nigeria. The family of four children, their parents and an uncle were kidnapped in Waza National Park in northern Cameroon, situated near the border with Nigeria. One of the captive men read a statement demanding that Nigeria and Cameroon free jailed members of Boko Haram.
Photos: Boko Haram: Nigeria's crisis
A French family kidnapped February 19, 2013, in northern Cameroon is released after two months in captivity in Nigeria. The family of four children, their parents and an uncle were kidnapped in Waza National Park in northern Cameroon, situated near the border with Nigeria. One of the captive men read a statement demanding that Nigeria and Cameroon free jailed members of Boko Haram.
PHOTO: Maxppp/Landov
A soldier stands in front of a damaged wall and the body of a prison officer killed during an attack on a prison in the northeastern Nigerian town of Bama on May 7, 2013. Two soldiers were killed during coordinated attacks on multiple targets. Nigeria
Photos: Boko Haram: Nigeria's crisis
A soldier stands in front of a damaged wall and the body of a prison officer killed during an attack on a prison in the northeastern Nigerian town of Bama on May 7, 2013. Two soldiers were killed during coordinated attacks on multiple targets. Nigeria's military said more than 100 Boko Haram militants carried out the attack.
PHOTO: STRINGER/AFP/Getty Images
A deserted student hostel is shown on August 6, 2013, after gunmen stormed a school in Yobe state, killing 20 students and a teacher, state media reported.
Photos: Boko Haram: Nigeria's crisis
A deserted student hostel is shown on August 6, 2013, after gunmen stormed a school in Yobe state, killing 20 students and a teacher, state media reported.
PHOTO: AMINU ABUBAKAR/AFP/Getty Images
A photograph made available by the Nigerian army on August 13, 2013, shows improvised explosive devices, bomb-making materials and detonators seized from a Boko Haram hideout. Gunmen attacked a mosque in Nigeria with automatic weapons on August 11, 2013, killing at least 44 people.
Photos: Boko Haram: Nigeria's crisis
A photograph made available by the Nigerian army on August 13, 2013, shows improvised explosive devices, bomb-making materials and detonators seized from a Boko Haram hideout. Gunmen attacked a mosque in Nigeria with automatic weapons on August 11, 2013, killing at least 44 people.
PHOTO: Deji Yake/EPA/LANDOV
Nigerian students from Jos Polytechnic walk on campus in Jos, Nigeria, on September 30, 2013. Under the cover of darkness, gunmen approached a college dormitory in a rural Nigerian town and opened fire on students who were sleeping. At least 40 students died, according to the News Agency of Nigeria.
Photos: Boko Haram: Nigeria's crisis
Nigerian students from Jos Polytechnic walk on campus in Jos, Nigeria, on September 30, 2013. Under the cover of darkness, gunmen approached a college dormitory in a rural Nigerian town and opened fire on students who were sleeping. At least 40 students died, according to the News Agency of Nigeria.
PHOTO: Ruth McDowall/EPA/LANDOV
Soldiers stand outside the 79 Composite Group Air Force base that was attacked earlier in Maiduguri on December 2, 2013. Hundreds of Boko Haram militants attacked an Air Force base and a military checkpoint, according to government officials.
Photos: Boko Haram: Nigeria's crisis
Soldiers stand outside the 79 Composite Group Air Force base that was attacked earlier in Maiduguri on December 2, 2013. Hundreds of Boko Haram militants attacked an Air Force base and a military checkpoint, according to government officials.
PHOTO: STRINGER/AFP/Getty Images
Catholic priest Georges Vandenbeusch speaks to reporters outside Paris after his release on January 1, 2014. Vandenbeusch was snatched from his parish church in Cameroon on November 13. Boko Haram claimed responsibility for kidnapping the priest.
Photos: Boko Haram: Nigeria's crisis
Catholic priest Georges Vandenbeusch speaks to reporters outside Paris after his release on January 1, 2014. Vandenbeusch was snatched from his parish church in Cameroon on November 13. Boko Haram claimed responsibility for kidnapping the priest.
PHOTO: ETIENNE LAURENT/EPA/LANDOV
A man receives treatment at Konduga specialist hospital after a gruesome attack on January 26, 2014. It was suspected that Boko Haram militants opened fire on a village market and torched homes in the village of Kawuri, killing at least 45 people.
Photos: Boko Haram: Nigeria's crisis
A man receives treatment at Konduga specialist hospital after a gruesome attack on January 26, 2014. It was suspected that Boko Haram militants opened fire on a village market and torched homes in the village of Kawuri, killing at least 45 people.
PHOTO: Jossy Ola/ap
Police officers stand guard in front of the burned remains of homes and businesses in the village of Konduga on February 12, 2014. Suspected Boko Haram militants torched houses in the village, killing at least 23 people, according to the governor of Borno state on February 11.
Photos: Boko Haram: Nigeria's crisis
Police officers stand guard in front of the burned remains of homes and businesses in the village of Konduga on February 12, 2014. Suspected Boko Haram militants torched houses in the village, killing at least 23 people, according to the governor of Borno state on February 11.
PHOTO: STRINGER/AFP/GETTY IMAGES
Yobe state Gov. Ibrahim Gaidam, left, looks at the bodies of students inside an ambulance outside a mosque in Damaturu. At least 29 students died in an attack on a federal college in Buni Yadi, near the capital of Yobe state, Nigeria
Photos: Boko Haram: Nigeria's crisis
Yobe state Gov. Ibrahim Gaidam, left, looks at the bodies of students inside an ambulance outside a mosque in Damaturu. At least 29 students died in an attack on a federal college in Buni Yadi, near the capital of Yobe state, Nigeria's military said on February 26, 2014. Authorities suspect Boko Haram carried out the assault in which several buildings were also torched.
PHOTO: ap
Rescue workers try to put out a fire after a bomb exploded at the busiest roundabout near the crowded Monday Market in Maiduguri on July 1, 2014.
Photos: Boko Haram: Nigeria's crisis
Rescue workers try to put out a fire after a bomb exploded at the busiest roundabout near the crowded Monday Market in Maiduguri on July 1, 2014.
PHOTO: STRINGER/AFP/Getty Images
Police in riot gear block a route in Abuja on October 14, 2014, during a demonstration calling on the Nigerian government to rescue schoolgirls kidnapped by Boko Haram. In April, more than 200 girls were abducted from their boarding school in northeastern Nigeria, officials and witnesses said.
Photos: Boko Haram: Nigeria's crisis
Police in riot gear block a route in Abuja on October 14, 2014, during a demonstration calling on the Nigerian government to rescue schoolgirls kidnapped by Boko Haram. In April, more than 200 girls were abducted from their boarding school in northeastern Nigeria, officials and witnesses said.
PHOTO: Olamikan Gbemiga/AP

Story highlights

NEW: Spokesman encourages potential fighters to go to Africa if they cannot get to Iraq or Syria

Abu Bakr al-Baghdadi's spokesman congratulated "our jihadi brothers" in western Africa

Boko Haram's leader had extended his pledge to be an ally in an audio message last week

(CNN) —  

In an audio message purportedly from an ISIS spokesman, the group announced that a pledge of allegiance from Nigerian-based Boko Haram has been accepted by ISIS leader Abu Bakr al-Baghdadi.

ISIS supporters posted the audio online. CNN cannot independently verify the 28-minute message.

The message says that ISIS, which calls itself the Islamic State, has expanded to western Africa and congratulated “our jihadi brothers” there.

An ISIS spokesman encouraged people to join fighters in Africa if they cannot make it to Iraq or Syria.

Wounded passengers are treated following a suicide bombing at the Brussels Airport on March 22, 2016. The attacks on the airport and a subway killed 32 people and wounded more than 300. ISIS claims its "fighters" launched the attacks in the Belgian capital.
Photos: The ISIS terror threat
Wounded passengers are treated following a suicide bombing at the Brussels Airport on March 22, 2016. The attacks on the airport and a subway killed 32 people and wounded more than 300. ISIS claims its "fighters" launched the attacks in the Belgian capital.
PHOTO: Ketevan Kardava/Getty Images
Syrians gather at the site of a double car bomb attack in the Al-Zahraa neighborhood of the Homs, Syria, on February 21, 2016. Multiple attacks in Homs and southern Damascus kill at least 122 and injure scores, according to the state-run SANA news agency. ISIS claimed responsibility.
Photos: The ISIS terror threat
Syrians gather at the site of a double car bomb attack in the Al-Zahraa neighborhood of the Homs, Syria, on February 21, 2016. Multiple attacks in Homs and southern Damascus kill at least 122 and injure scores, according to the state-run SANA news agency. ISIS claimed responsibility.
PHOTO: STRINGER/AFP/Getty Images
Syrian pro-government forces gather at the site of a deadly triple bombing Sunday, January 31, in the Damascus suburb of Sayeda Zeynab. ISIS claimed responsibility for the attack, according to a statement circulating online from supporters of the terrorist group.
Photos: The ISIS terror threat
Syrian pro-government forces gather at the site of a deadly triple bombing Sunday, January 31, in the Damascus suburb of Sayeda Zeynab. ISIS claimed responsibility for the attack, according to a statement circulating online from supporters of the terrorist group.
PHOTO: LOUAI BESHARA/AFP/Getty Images
Yemenis check the scene of a car bomb attack Sunday, December 6, in Aden, Yemen. Aden Gov. Jaafar Saad and six bodyguards died in the attack, for which the terror group ISIS claimed responsibility.
Photos: The ISIS terror threat
Yemenis check the scene of a car bomb attack Sunday, December 6, in Aden, Yemen. Aden Gov. Jaafar Saad and six bodyguards died in the attack, for which the terror group ISIS claimed responsibility.
PHOTO: Wael Qubady/AP
Investigators check the scene of a mosque attack Friday, November 27, in northern Bangladesh
Photos: The ISIS terror threat
Investigators check the scene of a mosque attack Friday, November 27, in northern Bangladesh's Bogra district. ISIS has claimed responsibility for the attack that left at least one person dead and three more wounded.
PHOTO: AP
Wounded people are helped outside the Bataclan concert hall in Paris following a series of coordinated attacks in the city on Friday, November 13. The militant group ISIS claimed responsibility for the attacks, which killed at least 130 people and wounded hundreds more.
Photos: The ISIS terror threat
Wounded people are helped outside the Bataclan concert hall in Paris following a series of coordinated attacks in the city on Friday, November 13. The militant group ISIS claimed responsibility for the attacks, which killed at least 130 people and wounded hundreds more.
PHOTO: YOAN VALAT/EPA/LANDOV
Emergency personnel and civilians gather at the site of a twin suicide bombing in Beirut, Lebanon, on Thursday, November 12. The bombings killed at least 43 people and wounded more than 200 more. ISIS appeared to claim responsibility in a statement posted on social media.
Photos: The ISIS terror threat
Emergency personnel and civilians gather at the site of a twin suicide bombing in Beirut, Lebanon, on Thursday, November 12. The bombings killed at least 43 people and wounded more than 200 more. ISIS appeared to claim responsibility in a statement posted on social media.
PHOTO: Bilal Hussein/AP
Smoke rises over the northern Iraqi town of Sinjar on November 12. Kurdish Iraqi fighters, backed by a U.S.-led air campaign, retook the strategic town, which ISIS militants overran last year. ISIS wants to create an Islamic state across Sunni areas of Iraq and Syria.
Photos: The ISIS terror threat
Smoke rises over the northern Iraqi town of Sinjar on November 12. Kurdish Iraqi fighters, backed by a U.S.-led air campaign, retook the strategic town, which ISIS militants overran last year. ISIS wants to create an Islamic state across Sunni areas of Iraq and Syria.
PHOTO: Bram Janssen/AP
Syrian government troops walk inside the Kweiras air base on Wednesday, November 11, after they broke a siege imposed by ISIS militants.
Photos: The ISIS terror threat
Syrian government troops walk inside the Kweiras air base on Wednesday, November 11, after they broke a siege imposed by ISIS militants.
PHOTO: SANA/AP
Members of the Egyptian military approach the wreckage of a Russian passenger plane Sunday, November 1, in Hassana, Egypt. The plane crashed the day before, killing all 224 people on board. ISIS claimed responsibility for downing the plane, but the group
Photos: The ISIS terror threat
Members of the Egyptian military approach the wreckage of a Russian passenger plane Sunday, November 1, in Hassana, Egypt. The plane crashed the day before, killing all 224 people on board. ISIS claimed responsibility for downing the plane, but the group's claim wasn't immediately verified.
PHOTO: Maxim Grigoriev/Russian Ministry for Emergency Situations/AP
An explosion rocks Kobani, Syria, during a reported car bomb attack by ISIS militants on Tuesday, October 20.
Photos: The ISIS terror threat
An explosion rocks Kobani, Syria, during a reported car bomb attack by ISIS militants on Tuesday, October 20.
PHOTO: Gokhan Sahin/Getty Images
Shiite fighters, fighting alongside Iraqi government forces, fire a rocket at ISIS militants as they advance toward the center of Baiji, Iraq, on Monday, October 19.
Photos: The ISIS terror threat
Shiite fighters, fighting alongside Iraqi government forces, fire a rocket at ISIS militants as they advance toward the center of Baiji, Iraq, on Monday, October 19.
PHOTO: AHMAD AL-RUBAYE/AFP/Getty Images
Smoke rises above a damaged building in Ramadi, Iraq, following a coalition airstrike against ISIS positions on Saturday, August 15.
Photos: The ISIS terror threat
Smoke rises above a damaged building in Ramadi, Iraq, following a coalition airstrike against ISIS positions on Saturday, August 15.
PHOTO: AP
Iraqi men look at damage following a bomb explosion that targeted a vegetable market in Baghdad on Thursday, August 13. ISIS claimed responsibility for the attack.
Photos: The ISIS terror threat
Iraqi men look at damage following a bomb explosion that targeted a vegetable market in Baghdad on Thursday, August 13. ISIS claimed responsibility for the attack.
PHOTO: AHMAD AL-RUBAYE/AFP/AFP/Getty Images
In this image taken from social media, an ISIS fighter holds the group
Photos: The ISIS terror threat
In this image taken from social media, an ISIS fighter holds the group's flag after the militant group overran the Syrian town of al-Qaryatayn on Thursday, August 6, the London-based Syrian Observatory for Human Rights reported. ISIS uses modern tools such as social media to promote reactionary politics and religious fundamentalism. Fighters are destroying holy sites and valuable antiquities even as their leaders propagate a return to the early days of Islam.
PHOTO: From ISIS
An ISIS fighter poses with spoils purportedly taken after capturing the Syrian town of al-Qaryatayn.
Photos: The ISIS terror threat
An ISIS fighter poses with spoils purportedly taken after capturing the Syrian town of al-Qaryatayn.
PHOTO: From ISIS
Smoke rises as Iraqi security forces bomb ISIS positions in the eastern suburbs of Ramadi, Iraq, on August 6.
Photos: The ISIS terror threat
Smoke rises as Iraqi security forces bomb ISIS positions in the eastern suburbs of Ramadi, Iraq, on August 6.
PHOTO: AP
Buildings reduced to piles of debris can be seen in the eastern suburbs of Ramadi on August 6.
Photos: The ISIS terror threat
Buildings reduced to piles of debris can be seen in the eastern suburbs of Ramadi on August 6.
PHOTO: AP
The governor of the Asir region in Saudi Arabia, Prince Faisal bin Khaled bin Abdulaziz, left, visits a man who was wounded in a suicide bombing attack on a mosque in Abha, Saudi Arabia, on August 6. ISIS claimed responsibility for the explosion, which killed at least 13 people and injured nine others.
Photos: The ISIS terror threat
The governor of the Asir region in Saudi Arabia, Prince Faisal bin Khaled bin Abdulaziz, left, visits a man who was wounded in a suicide bombing attack on a mosque in Abha, Saudi Arabia, on August 6. ISIS claimed responsibility for the explosion, which killed at least 13 people and injured nine others.
PHOTO: Saudi Press Agency/AP
Saudi officials and investigators check the inside of the mosque on August 6.
Photos: The ISIS terror threat
Saudi officials and investigators check the inside of the mosque on August 6.
PHOTO: Saudi Press Agency/AP
Mourners in Gaziantep, Turkey, grieve over a coffin Tuesday, July 21, during a funeral ceremony for the victims of a suspected ISIS suicide bomb attack. That bombing killed at least 31 people in Suruc, a Turkish town that borders Syria. Turkish authorities blamed ISIS for the attack.
Photos: The ISIS terror threat
Mourners in Gaziantep, Turkey, grieve over a coffin Tuesday, July 21, during a funeral ceremony for the victims of a suspected ISIS suicide bomb attack. That bombing killed at least 31 people in Suruc, a Turkish town that borders Syria. Turkish authorities blamed ISIS for the attack.
PHOTO: Gokhan Sahin/Getty Images
Protesters in Istanbul carry anti-ISIS banners and flags to show support for victims of the Suruc suicide blast during a demonstration on Monday, July 20.
Photos: The ISIS terror threat
Protesters in Istanbul carry anti-ISIS banners and flags to show support for victims of the Suruc suicide blast during a demonstration on Monday, July 20.
PHOTO: YASIN AKGUL/AFP/Getty Images
People in Ashmoun, Egypt, carry the coffin for 1st Lt. Mohammed Ashraf, who was killed when the ISIS militant group attacked Egyptian military checkpoints on Wednesday, July 1. At least 17 soldiers were reportedly killed, and 30 were injured.
Photos: The ISIS terror threat
People in Ashmoun, Egypt, carry the coffin for 1st Lt. Mohammed Ashraf, who was killed when the ISIS militant group attacked Egyptian military checkpoints on Wednesday, July 1. At least 17 soldiers were reportedly killed, and 30 were injured.
PHOTO: Ashour Abosalm/AP
Syrians wait near the Turkish border during clashes between ISIS and Kurdish armed groups in Kobani, Syria, on Thursday, June 25. The photo was taken in Sanliurfa, Turkey. ISIS militants disguised as Kurdish security forces infiltrated Kobani on Thursday and killed "many civilians," said a spokesman for the Kurds in Kobani.
Photos: The ISIS terror threat
Syrians wait near the Turkish border during clashes between ISIS and Kurdish armed groups in Kobani, Syria, on Thursday, June 25. The photo was taken in Sanliurfa, Turkey. ISIS militants disguised as Kurdish security forces infiltrated Kobani on Thursday and killed "many civilians," said a spokesman for the Kurds in Kobani.
PHOTO: Halil Fidan/Anadolu Agency/Getty Images
Residents examine a damaged mosque after an Iraqi Air Force bombing in the ISIS-seized city of Falluja, Iraq, on Sunday, May 31. At least six were killed and nine others wounded during the bombing.
Photos: The ISIS terror threat
Residents examine a damaged mosque after an Iraqi Air Force bombing in the ISIS-seized city of Falluja, Iraq, on Sunday, May 31. At least six were killed and nine others wounded during the bombing.
PHOTO: Sami Jawad/Xinhua/SIPA
People search through debris after an explosion at a Shiite mosque in Qatif, Saudi Arabia, on Friday, May 22. ISIS claimed responsibility for the attack, according to tweets from ISIS supporters, which included a formal statement from ISIS detailing the operation.
Photos: The ISIS terror threat
People search through debris after an explosion at a Shiite mosque in Qatif, Saudi Arabia, on Friday, May 22. ISIS claimed responsibility for the attack, according to tweets from ISIS supporters, which included a formal statement from ISIS detailing the operation.
PHOTO: EPA/STR/LANDOV
Iraqi soldiers fire their weapons toward ISIS group positions in the Garma district, west of the Iraqi capital of Baghdad, on Sunday, April 26. Pro-government forces said they had recently made advances on areas held by Islamist jihadists.
Photos: The ISIS terror threat
Iraqi soldiers fire their weapons toward ISIS group positions in the Garma district, west of the Iraqi capital of Baghdad, on Sunday, April 26. Pro-government forces said they had recently made advances on areas held by Islamist jihadists.
PHOTO: AHMAD AL-RUBAYE/AFP/Getty Images
A member of Afghanistan
Photos: The ISIS terror threat
A member of Afghanistan's security forces stands at the site where a suicide bomber on a motorbike blew himself up in front of the Kabul Bank in Jalalabad, Afghanistan, on Saturday, April 18. ISIS claimed responsibility for the attack. The explosion killed at least 33 people and injured more than 100 others, a public health spokesman said.
PHOTO: Stringer/AP
Iraqi counterterrorism forces patrol in Ramadi on April 18.
Photos: The ISIS terror threat
Iraqi counterterrorism forces patrol in Ramadi on April 18.
PHOTO: Stringer/AP
Thousands of Iraqis cross a bridge over the Euphrates River to Baghdad as they flee Ramadi on Friday, April 17.
Photos: The ISIS terror threat
Thousands of Iraqis cross a bridge over the Euphrates River to Baghdad as they flee Ramadi on Friday, April 17.
PHOTO: Ali Mohammed/Anadolu Agency/Getty Images
Yazidis embrace after being released by ISIS south of Kirkuk, Iraq, on Wednesday, April 8. ISIS released more than 200 Yazidis, a minority group whose members were killed, captured and displaced when the Islamist terror organization overtook their towns in northern Iraq last summer, officials said.
Photos: The ISIS terror threat
Yazidis embrace after being released by ISIS south of Kirkuk, Iraq, on Wednesday, April 8. ISIS released more than 200 Yazidis, a minority group whose members were killed, captured and displaced when the Islamist terror organization overtook their towns in northern Iraq last summer, officials said.
PHOTO: Ali Mukarrem Garip/Anadolu Agency/Getty Images
Kurdish Peshmerga forces help Yazidis as they arrive at a medical center in Altun Kupri, Iraq, on April 8.
Photos: The ISIS terror threat
Kurdish Peshmerga forces help Yazidis as they arrive at a medical center in Altun Kupri, Iraq, on April 8.
PHOTO: SAFIN HAMED/AFP/Getty Images
A Yazidi woman mourns for the death of her husband and children by ISIS after being released south of Kirkuk on April 8. ISIS is known for killing dozens of people at a time and carrying out public executions, crucifixions and other acts.
Photos: The ISIS terror threat
A Yazidi woman mourns for the death of her husband and children by ISIS after being released south of Kirkuk on April 8. ISIS is known for killing dozens of people at a time and carrying out public executions, crucifixions and other acts.
PHOTO: Feriq Ferec/Anadolu Agency/Getty Images
People in Tikrit inspect what used to be a palace of former President Saddam Hussein on April 3.
Photos: The ISIS terror threat
People in Tikrit inspect what used to be a palace of former President Saddam Hussein on April 3.
PHOTO: Khalid Mohammed/AP
On April 1, Shiite militiamen celebrate the retaking of Tikrit, which had been under ISIS control since June. The push into Tikrit came days after U.S.-led airstrikes targeted ISIS bases around the city.
Photos: The ISIS terror threat
On April 1, Shiite militiamen celebrate the retaking of Tikrit, which had been under ISIS control since June. The push into Tikrit came days after U.S.-led airstrikes targeted ISIS bases around the city.
PHOTO: AHMAD AL-RUBAYE/AFP/Getty Images
Iraqi security forces launch a rocket against ISIS positions in Tikrit on Monday, March 30.
Photos: The ISIS terror threat
Iraqi security forces launch a rocket against ISIS positions in Tikrit on Monday, March 30.
PHOTO: Khalid Mohammed/AP
The parents of 19-year-old Mohammed Musallam react at the family
Photos: The ISIS terror threat
The parents of 19-year-old Mohammed Musallam react at the family's home in the East Jerusalem Jewish settlement of Neve Yaakov on Tuesday, March 10. ISIS released a video purportedly showing a young boy executing Musallam, an Israeli citizen of Palestinian descent who ISIS claimed infiltrated the group in Syria to spy for the Jewish state. Musallam's family told CNN that he had no ties with the Mossad, Israel's spy agency, and had, in fact, been recruited by ISIS.
PHOTO: Ahmed Gharabli/AFP/Getty Images
Iraqi Shiite fighters cover their ears as a rocket is launched during a clash with ISIS militants in the town of Al-Alam, Iraq, on Monday, March 9.
Photos: The ISIS terror threat
Iraqi Shiite fighters cover their ears as a rocket is launched during a clash with ISIS militants in the town of Al-Alam, Iraq, on Monday, March 9.
PHOTO: Thaier Al-Sudani/Reuters
Displaced Assyrian women who fled their homes due to ISIS attacks pray at a church on the outskirts of Damascus, Syria, on Sunday, March 1. ISIS militants abducted at least 220 Assyrians in Syria.
Photos: The ISIS terror threat
Displaced Assyrian women who fled their homes due to ISIS attacks pray at a church on the outskirts of Damascus, Syria, on Sunday, March 1. ISIS militants abducted at least 220 Assyrians in Syria.
PHOTO: LOUAI BESHARA/AFP/Getty Images
Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on Wednesday, February 4. Al-Kasasbeh
Photos: The ISIS terror threat
Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on Wednesday, February 4. Al-Kasasbeh's son, Jordanian pilot Moath al-Kasasbeh, was burned alive in a video that was recently released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.
PHOTO: Nasser Nasser/AP
A Kurdish marksman looks over a destroyed area of Kobani on Friday, January 30, after the city had been liberated from the ISIS militant group. The Syrian city, also known as Ayn al-Arab, had been under assault by ISIS since mid-September.
Photos: The ISIS terror threat
A Kurdish marksman looks over a destroyed area of Kobani on Friday, January 30, after the city had been liberated from the ISIS militant group. The Syrian city, also known as Ayn al-Arab, had been under assault by ISIS since mid-September.
PHOTO: BULENT KILIC/AFP/Getty Images
Kurdish people celebrate in Suruc, Turkey, near the Turkish-Syrian border, after ISIS militants were expelled from Kobani on Tuesday, January 27.
Photos: The ISIS terror threat
Kurdish people celebrate in Suruc, Turkey, near the Turkish-Syrian border, after ISIS militants were expelled from Kobani on Tuesday, January 27.
PHOTO: BULENT KILIC/AFP/Getty Images
Collapsed buildings are seen in Kobani on January 27 after Kurdish forces took control of the town from ISIS.
Photos: The ISIS terror threat
Collapsed buildings are seen in Kobani on January 27 after Kurdish forces took control of the town from ISIS.
PHOTO: Rauf Maltas/Anadolu Agency/Getty Images
Junko Ishido, mother of Japanese journalist Kenji Goto, reacts during a news conference in Tokyo on Friday, January 23. ISIS would later kill Goto and another Japanese hostage, Haruna Yukawa.
Photos: The ISIS terror threat
Junko Ishido, mother of Japanese journalist Kenji Goto, reacts during a news conference in Tokyo on Friday, January 23. ISIS would later kill Goto and another Japanese hostage, Haruna Yukawa.
PHOTO: Toru Hanai/Reuters/LANDOV
ISIS militants are seen through a rifle
Photos: The ISIS terror threat
ISIS militants are seen through a rifle's scope during clashes with Peshmerga fighters in Mosul, Iraq, on Wednesday, January 21.
PHOTO: Emrah Yorulmaz/Anadolu Agency/Getty Images
An elderly Yazidi man arrives in Kirkuk after being released by ISIS on Saturday, January 17. The militant group released about 200 Yazidis who were held captive for five months in Iraq. Almost all of the freed prisoners were in poor health and bore signs of abuse and neglect, Kurdish officials said.
Photos: The ISIS terror threat
An elderly Yazidi man arrives in Kirkuk after being released by ISIS on Saturday, January 17. The militant group released about 200 Yazidis who were held captive for five months in Iraq. Almost all of the freed prisoners were in poor health and bore signs of abuse and neglect, Kurdish officials said.
PHOTO: AP
Smoke billows behind an ISIS sign during an Iraqi military operation to regain control of the town of Sadiyah, about 95 kilometers (60 miles) north of Baghdad, on Tuesday, November 25.
Photos: The ISIS terror threat
Smoke billows behind an ISIS sign during an Iraqi military operation to regain control of the town of Sadiyah, about 95 kilometers (60 miles) north of Baghdad, on Tuesday, November 25.
PHOTO: AP
Fighters from the Free Syrian Army and the Kurdish People
Photos: The ISIS terror threat
Fighters from the Free Syrian Army and the Kurdish People's Protection Units join forces to fight ISIS in Kobani on Wednesday, November 19.
PHOTO: Jake Simkin/AP
A picture taken from Turkey shows smoke rising after ISIS militants fired mortar shells toward an area controlled by Syrian Kurdish fighters near Kobani on Monday, November 3.
Photos: The ISIS terror threat
A picture taken from Turkey shows smoke rising after ISIS militants fired mortar shells toward an area controlled by Syrian Kurdish fighters near Kobani on Monday, November 3.
PHOTO: ULAS YUNUS TOSUN/EPA/Landov
Iraqi special forces search a house in Jurf al-Sakhar, Iraq, on Thursday, October 30, after retaking the area from ISIS.
Photos: The ISIS terror threat
Iraqi special forces search a house in Jurf al-Sakhar, Iraq, on Thursday, October 30, after retaking the area from ISIS.
PHOTO: HAIDAR HAMDANI/AFP/Getty Images
ISIS militants stand near the site of an airstrike near the Turkey-Syria border on Thursday, October 23. The United States and several Arab nations have been bombing ISIS targets in Syria to take out the militant group
Photos: The ISIS terror threat
ISIS militants stand near the site of an airstrike near the Turkey-Syria border on Thursday, October 23. The United States and several Arab nations have been bombing ISIS targets in Syria to take out the militant group's ability to command, train and resupply its fighters.
PHOTO: BULENT KILIC/AFP/Getty Images
Kurdish fighters walk to positions as they combat ISIS forces in Kobani on Sunday, October 19.
Photos: The ISIS terror threat
Kurdish fighters walk to positions as they combat ISIS forces in Kobani on Sunday, October 19.
PHOTO: Gokhan Sahin/Getty Images
Heavy smoke rises in Kobani following an airstrike by the U.S.-led coalition on October 18.
Photos: The ISIS terror threat
Heavy smoke rises in Kobani following an airstrike by the U.S.-led coalition on October 18.
PHOTO: Gokhan Sahin/Getty Images
Cundi Minaz, a female Kurdish fighter, is buried in a cemetery in the southeastern Turkish town of Suruc on Tuesday, October 14. Minaz was reportedly killed during clashes with ISIS militants in nearby Kobani.
Photos: The ISIS terror threat
Cundi Minaz, a female Kurdish fighter, is buried in a cemetery in the southeastern Turkish town of Suruc on Tuesday, October 14. Minaz was reportedly killed during clashes with ISIS militants in nearby Kobani.
PHOTO: Gokhan Sahin/Getty Images
Kiymet Ergun, a Syrian Kurd, celebrates in Mursitpinar, Turkey, after an airstrike by the U.S.-led coalition in Kobani on Monday, October 13.
Photos: The ISIS terror threat
Kiymet Ergun, a Syrian Kurd, celebrates in Mursitpinar, Turkey, after an airstrike by the U.S.-led coalition in Kobani on Monday, October 13.
PHOTO: Lefteris Pitarakis/ap
Alleged ISIS militants stand next to an ISIS flag atop a hill in Kobani on Monday, October 6.
Photos: The ISIS terror threat
Alleged ISIS militants stand next to an ISIS flag atop a hill in Kobani on Monday, October 6.
PHOTO: Aris Messinis/AFP/Getty Images
A Kurdish Peshmerga soldier who was wounded in a battle with ISIS is wheeled to the Zakho Emergency Hospital in Duhuk, Iraq, on Tuesday, September 30.
Photos: The ISIS terror threat
A Kurdish Peshmerga soldier who was wounded in a battle with ISIS is wheeled to the Zakho Emergency Hospital in Duhuk, Iraq, on Tuesday, September 30.
PHOTO: Hadi Mizban/AP
Syrian Kurds wait near a border crossing in Suruc as they wait to return to their homes in Kobani on Sunday, September 28.
Photos: The ISIS terror threat
Syrian Kurds wait near a border crossing in Suruc as they wait to return to their homes in Kobani on Sunday, September 28.
PHOTO: MURAD SEZER/Reuters/Landov
A elderly man is carried after crossing the Syria-Turkey border near Suruc on Saturday, September 20.
Photos: The ISIS terror threat
A elderly man is carried after crossing the Syria-Turkey border near Suruc on Saturday, September 20.
PHOTO: BULENT KILIC/AFP/Getty Images
A Kurdish Peshmerga fighter launches mortar shells toward ISIS militants in Zumar, Iraq, on Monday, September 15.
Photos: The ISIS terror threat
A Kurdish Peshmerga fighter launches mortar shells toward ISIS militants in Zumar, Iraq, on Monday, September 15.
PHOTO: AHMED JADALLAH/Reuters/Landov
Kurdish Peshmerga fighters fire at ISIS militant positions from their position on the top of Mount Zardak, east of Mosul, Iraq, on Tuesday, September 9.
Photos: The ISIS terror threat
Kurdish Peshmerga fighters fire at ISIS militant positions from their position on the top of Mount Zardak, east of Mosul, Iraq, on Tuesday, September 9.
PHOTO: JM LOPEZ/AFP/Getty Images
Displaced Iraqis receive clothes from a charity at a refugee camp near Feeshkhabour, Iraq, on Tuesday, August 19.
Photos: The ISIS terror threat
Displaced Iraqis receive clothes from a charity at a refugee camp near Feeshkhabour, Iraq, on Tuesday, August 19.
PHOTO: Khalid Mohammed/AP
Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and some other Yazidi people are flown to safety Monday, August 11, after a dramatic rescue operation at Iraq
Photos: The ISIS terror threat
Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and some other Yazidi people are flown to safety Monday, August 11, after a dramatic rescue operation at Iraq's Mount Sinjar. A CNN crew was on the flight, which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. But only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.
PHOTO: Warzer Jaff/CNN
Thousands of Yazidis are escorted to safety by Kurdish Peshmerga forces and a People
Photos: The ISIS terror threat
Thousands of Yazidis are escorted to safety by Kurdish Peshmerga forces and a People's Protection Unit in Mosul on Saturday, August 9.
PHOTO: Emrah Yorulmaz/Anadolu Agency/Getty Images
Thousands of Yazidi and Christian people flee Mosul on Wednesday, August 6, after the latest wave of ISIS advances.
Photos: The ISIS terror threat
Thousands of Yazidi and Christian people flee Mosul on Wednesday, August 6, after the latest wave of ISIS advances.
PHOTO: Mustafa Kerim/Anadolu Agency/Getty Images
A Baiji oil refinery burns after an alleged ISIS attack in northern Selahaddin, Iraq, on Thursday, July 31.
Photos: The ISIS terror threat
A Baiji oil refinery burns after an alleged ISIS attack in northern Selahaddin, Iraq, on Thursday, July 31.
PHOTO: Stringer/Anadolu Agency/Getty mages
A Syrian rebel fighter lies on a stretcher at a makeshift hospital in Douma, Syria, on Wednesday, July 9. He was reportedly injured while fighting ISIS militants.
Photos: The ISIS terror threat
A Syrian rebel fighter lies on a stretcher at a makeshift hospital in Douma, Syria, on Wednesday, July 9. He was reportedly injured while fighting ISIS militants.
PHOTO: ABD DOUMANY/AFP/Getty Images
Children stand next to a burnt vehicle during clashes between Iraqi security forces and ISIS militants in Mosul on Tuesday, June 10.
Photos: The ISIS terror threat
Children stand next to a burnt vehicle during clashes between Iraqi security forces and ISIS militants in Mosul on Tuesday, June 10.
PHOTO: STRINGER/IRAQ/reuters/LANDOV

Boko Haram’s leader, Abubakar Shekau, announced in an audio message last week that his terror group wanted to join ISIS.

Jacob Zenn, a terror expert who lives in Nigeria, told CNN on Saturday the alliance would make sense for both groups.

“Boko Haram will get legitimacy, which will help its recruiting, funding and logistics as it expands,” Zenn said. “It will also get guidance from ISIS in media warfare and propaganda. Previously Boko Haram was a sort of outcast in the global Jihadi community. Now it is perhaps ISIS’s biggest affiliate.

“ISIS gets more international legitimacy as a global caliphate.”

Years of terror

Boko Haram, whose name translates as “Western education is sin,” has been waging a yearslong campaign of terror aimed at instituting its extreme version of Sharia law.

Boko Haram has terrorized northern Nigeria regularly since 2009, attacking police, schools, churches, mosques and civilians. It has also kidnapped students, including more than 200 schoolgirls who were abducted in April and remain missing.

Much of this violence has taken place in Nigeria. But neighboring countries, such as Cameroon and Chad, have also been hit increasingly hard.

What Boko Haram’s pledge of allegiance to ISIS means

CNN’s Paul Cruickshank contributed to this report.