Jos, Nigeria (CNN) -- A government official condemned Monday the series of Christmas Day attacks on churches in Nigeria that killed 35 people, blaming an extremist group that has claimed responsibility for similar attacks in the last two years.
"The latest mindless and cowardly attacks by Boko Haram members specifically directed at churches were premeditated," said retired Gen. Andrew Azazi, the national security adviser to President Goodluck Jonathan, in a statement. "Only last week, five improvised explosive devices were recovered in five churches at Mubi in Adamawa State."
The Boko Haram sect claimed responsibility for the attacks, government officials said. In the past, the group has targeted Christians and Muslims it considered insufficiently Islamic.
In the bloodiest of Sunday's attacks on churches in five cities, 32 people were killed as services ended at St. Theresa's Catholic Church in Madalla in Niger State, Azazi said. Two people have been arrested, he added.
Olusegun Okebiorun, controller-general of Nigeria's fire service, said that, in addition to the fatalities, 65 people were wounded in Madalla, which is located west of the capital city of Abuja.
Attacks in the central Nigerian city of Jos in Plateau State northeast of the capital followed the same pattern, Azazi said.
Two blasts targeted the Mountain of Fire Ministries church in Jos, said journalist Hassan John, who witnessed the carnage. No one was killed in the bombings, but a police officer who got into a gun battle with attackers died of his wounds, John said, citing officials.
Police arrested four people and recovered four unexploded devices, Nigerian state television reported.
The cities of Kano, Damaturu and Gadaka were also struck Sunday, John said.
Officials said three people were killed in the blast in Damaturu, a northern town in Yobe state, John said. Also in Damaturu, a police station and a state security building were bombed, said an aid worker who, citing security concerns, asked not to be identified.
In Yobe, security forces stopped a vehicle that was carrying a bomb, which detonated, killing "the criminals" and three security operatives, Azazi said.
"We renew our appeal to all Nigerians that this is not a fight between security forces and some dissident elements," he said. "It is a conflict between some misguided extremists in our midst and the rest of our society, because the victims are not confined to any ethnic boundary. We must cooperate to fish them out. And because our cause is just and our collective resolve is stronger, together we shall prevail."
The blasts mark the second consecutive holiday season that bombs have hit Christian houses of worship in the west African nation. In 2010, five churches in Jos were attacked on Christmas Eve. The blasts killed dozens in Jos, which lies on a faith-based fault line between the Muslim-dominated north and the mainly Christian south. CNN.com: Al Qaeda-linked group claims responsibility for bombing
In a statement issued late Sunday, Jonathan called the bombings "a dastardly act that must attract the rebuke of all peace-loving Nigerians."
In Washington, the White House said U.S. officials would help Nigeria pursue those behind "what initially appear to be terrorist acts."
"We condemn this senseless violence and tragic loss of life on Christmas Day," White House spokesman Jay Carney said in a statement. "We offer our sincere condolences to the Nigerian people and especially those who lost family and loved ones."
U.N. Secretary-General Ban Ki-moon condemned the acts "in the strongest terms," his office said in a statement. He expressed his condolences to the Nigerian people and reiterated a call "for an end to all acts of sectarian violence in the country."
Nigeria is Africa's most populous nation and has the world's sixth-largest Christian population -- about 80.5 million people as of 2010, according to a report published this month by the Pew Forum on Religion & Public Life in Washington. That makes the country just over 50% Christian, according to Pew.
Boko Haram translates from the local Hausa as "Western education is outlawed." The group has morphed into an insurgency responsible for dozens of attacks in Nigeria in the last two years.
Boko Haram's targets include police outposts and churches as well as places associated with "Western influence."
CNN's Josh Levs, Richard Allen Greene, Esprit Smith, Karen Smith, Amir Ahmed and Hamdi Alkhshali contributed to this report.