RAWALPINDI, Pakistan (CNN) -- Pakistan's former Prime Minister Benazir Bhutto was assassinated Thursday after addressing a large gathering of her supporters.
The bomb explodes near Bhutto's vehicle following a political rally in Rawalpindi.
Bhutto died of a gunshot wound to the neck, the Pakistani Interior Ministry said. The attacker then blew himself up. The bomb attack killed at least 22 others, doctors said.
Video of the scene just moments before the explosion showed Bhutto stepping into a heavily guarded vehicle to leave the rally. Watch how the tragedy unfolded »
John Moore, a photographer for Getty Images, said Bhutto was standing through the sunroof of her vehicle, waving to supporters, when two shots rang out.
Bhutto fell back into the vehicle, and almost immediately a bomb blast rocked the scene, sending twisting metal and shrapnel into the crowd, he added.
Police sources told CNN the bomber, who was riding a motorcycle, blew himself up near Bhutto's vehicle. Watch aftermath of the attack.
Bhutto was rushed to Rawalpindi General Hospital -- less than two miles from the bombing scene -- where doctors pronounced her dead.
Her body was removed from the hospital -- carried above a crowd of supporters -- late Thursday night, and a Pakistan Air Force plane is flying the body to Sukkur, accompanied by her husband and three children, said Pakistan People's Party leader Sen. Safdar Abbasi.
Bhutto is scheduled to be buried in the ancestral graveyard of the Bhutto family at Gari-Khuda Baksh in Sindh province Friday afternoon, he added.
Chaos erupted at the hospital when former Prime Minister Nawaz Sharif arrived to pay his respects to Bhutto less than three hours after her death.
Hundreds of Bhutto supporters crammed into the entrance shouted and cried, some clutching their heads in pain and shock. Sharif called it "the saddest day" in Pakistan's history. "Something unthinkable has happened," he said. Watch Benazir Bhutto obituary »
Sharif said his party will boycott Pakistan's January 8 parliamentary elections in the wake of the assassination.
President Pervez Musharraf said the killers were the same extremists that Pakistan is fighting a war against, and announced three days of national mourning.
Police warned citizens to stay home as they expected rioting to break out in city streets in reaction to the death.
Rioters burned tires and blocked roads in Karachi and other cities, police sources said. Police fired on an angry mob, killing two people, in the city of Khairpur in the Sindh province, Geo TV reported.
Bhutto's husband issued a statement from his home in Dubai saying, "All I can say is we're devastated, it's a total shock." He arrived in Pakistan late Thursday.
President Bush said those responsible "must be brought to justice" and praised Bhutto as a woman who had "fought the forces of terror." He said: "She refused to allow assassins to dictate the course of her country."
The number of wounded was not immediately known. However, video of the scene showed ambulances lined up to take many to hospitals.
The assassination happened in Rawalpindi's Liaquat Bagh Park, named for Pakistan's first prime minister -- Liaquat Ali Khan -- who was assassinated in the same location in 1951.
The attack came just hours after four supporters of former Pakistan Prime Minister Nawaz Sharif died when members of another political party opened fire on them at a rally near the Islamabad airport Thursday, Pakistan police said.
Several other members of Sharif's party were wounded, police said.
Bhutto, who led Pakistan from 1988 to 1990 and was the first female prime minister of any Islamic nation, was participating in the parliamentary election set for January 8, hoping for a third term.
A terror attack targeting her motorcade in Karachi killed 136 people on the day she returned to Pakistan after eight years of self-imposed exile. View timeline. »
CNN's Mohsin Naqvi, who was at the scene of both bombings, said Thursday's blast was not as powerful as that October attack.
Thursday's attacks come less than two weeks after Pakistan President Pervez Musharraf lifted an emergency declaration he said was necessary to secure his country from terrorists.
Bhutto had been critical of what she believed was a lack of effort by Musharraf's government to protect her.
Two weeks after the October assassination attempt, she wrote a commentary for CNN.com in which she questioned why Pakistan investigators refused international offers of help in finding the attackers.
"The sham investigation of the October 19 massacre and the attempt by the ruling party to politically capitalize on this catastrophe are discomforting, but do not suggest any direct involvement by General Pervez Musharraf," Bhutto wrote. E-mail to a friend
CNN's Mohsin Naqvi contributed to this report