A Yemeni soldier detonated a bomb hidden in his military uniform during a rehearsal for a military parade, killing 96 fellow soldiers and wounding at least 200 on Monday in one of the deadliest attacks in the capital in years.
Al-Qaida's branch in Yemen claimed responsibility, saying in an emailed statement that the suicide attack was intended to avenge a U.S.-backed offensive against al-Qaida in a swath of southern Yemen seized by the militant movement last year.
The bombing left a scene of carnage, with scores of bleeding soldiers lying on the ground as ambulances rushed to the scene. Several severed heads were on the pavement amid large pools of blood and human remains.
"This is a real massacre," said Ahmed Sobhi, one of the soldiers who witnessed the blast. "This is unbelievable. I am still shaking. The place turned into hell. I thought this only happens in movies."
Al-Qaida said the bomber was targeting Yemen's defense minister, Maj. Gen. Mohammed Nasser Ahmed, who had arrived at the heavily secured city square to greet the assembled troops just minutes before the blast ripped through the area. He was unhurt.
Khaled Ali, another soldier, said the explosion was followed by heavy gunfire.
"In the mayhem, we were all running in all directions. I saw the guards of the minister surrounding him and forming a human cordon. They were firing in the air," he said.
The bombing comes as Yemeni President Abed Rabbo Mansour Hadi has been pressing ahead on two difficult fronts _ battling al-Qaida in the south and purging loyalists of ousted leader Ali Abdullah Saleh from military and security top posts.
Saleh stepped down in February as part of a U.S.-backed, power-transfer deal brokered by Gulf Arab countries aimed at ending political unrest in the country after a yearlong uprising. The deal gave Saleh immunity from prosecution in return for relinquishing his power.
Saleh originally appointed Ahmed to lead the defense ministry but recently has pressed from behind the scenes for his dismissal because Ahmed has been cooperating with Hadi.
Military officials said the bomber belonged to the Central Security, a paramilitary force commanded by Saleh's nephew Yahia Saleh. He detonated his explosives in the midst of the Central Security unit as it received orders to pass in front of the parade view stand where both the defense minister and the military chief of staff were sitting.
"They are playing their last cards and blackmailing the new leadership," said political analyst Abdel-Bari Taher. "This is one desperate attempt by both al-Qaida and Saleh's regime to survive."
Shortly after the attack, Hadi demoted two of Saleh's relatives, including Yahia, from their top positions in the Central Security forces and the Interior Ministry.
A statement in Hadi's name read on state TV said, "The war on terrorism will continue until we win, whatever the sacrifices are."
"We are speeding up the restructuring of the army to bring back stability to the country, which was on a brink of all-out war," the statement said.
Soldiers who were at the site told The Associated Press that the bomber could not have been an outsider. The soldiers said their commanders selected them from different branches of the military to participate in the parade, and that they had been practicing together for a week.
The site of the attack, close to the presidential palace, had been sealed off by Republican Guard forces for the previous 24 hours in preparation for the National Day celebrations on Tuesday. No cars or pedestrians were allowed to enter. The Republican Guard is led by Saleh's son and one-time heir apparent, Ahmed Saleh.
Saleh, who ruled Yemen for some 33 years, was a key partner with the U.S., which poured in millions of dollars in aid and training to fight al-Qaida.
However, Saleh was seen as unreliable. He directed funds toward bolstering units led by family members and die-hard loyalists. He often struck deals with Islamic militants, even releasing some from prison, as a tool to play his foes off against each other.
During the 1990s, Saleh ordered integration of Yemeni Islamic militants in the army ranks after their return from the fight against the Soviets in Afghanistan.
In its statement Monday, al-Qaida said "our main battle is against America so don't stand as a deterrent in the way or be tools or soldiers commanded by John Brennan and the American ambassador in Sanaa," a reference to the White House's top counterterrorism adviser who visited Yemen last week.
The White House said Brennan called Yemen's president to condemn the attack and offer U.S. assistance in the investigation.
The attack came one week after the leader of al-Qaida, Ayman al-Zawahri, released an audio recording online scolding Hadi and describing him as a U.S. agent and a traitor.
The Obama administration has thrown its support behind Hadi and his fight against al-Qaida in the Arabian Peninsula, which was behind three failed bomb plots on U.S. soil.
With U.S. help, Yemen's military launched a wide and so far a successful offensive on several fronts in the south over the past week. Yemeni officials said earlier that nearly 60 U.S. troops were steering the offensive at the al-Annad air base in Lahj province.
The Pentagon also confirmed Monday that three civilian contractors helping train Yemen's coast guard were attacked in Yemen. Cmdr. Bill Speaks, a Defense Department spokesman, said that injuries were minor.
The three were traveling in a car in the Red Sea port city of Hodeida on Sunday, when they were shot at by militants in another vehicle.
Al-Qaida claimed responsibility for that attack as well.
"After we have witnessed the American involvement in Yemen, we call upon all free Muslims in Yemen to target Americans everywhere," the group said. It was not possible to verify the authenticity of either statement attributed to al-Qaida.
Yemen, the ancestral homeland of Osama bin Laden, was the site of the 2000 bombing of the USS Cole, which killed 17 American sailors. There have also been a spate of assaults on the U.S. Embassy in Sanaa, including a 2008 bombing that killed 10 Yemeni guards and four civilians.
Michael reported from Cairo, Egypt. Sarah El Deeb contributed to this report from Cairo.