The attack started with a car bomb explosion, then militants exchanged heavy gunfire with the guards at the Sanaa Central Prison, and a number of prisoners fled amid the chaos, according to SABA. A security official said authorities suspect it was an inside job.
Among the 29 who fled, 19 are convicted al-Qiada prisoners including those plotting the assassinations of Yemeni President Abed Rabbo Mansour Hadi and western diplomats, the official said. He said those killed in the exchange of gunfire were mostly security forces.
Witnesses said earlier that explosions rocked the capital and smoke billowed into the sky. Security forces and army troops have been deployed to the site of the attack and sealed off the whole area. The prison, housing thousands of inmates, is on the main road leading to the airport, which was closed.
Security officials say that the attackers came in three groups and three cars, including the car bomb. One group detonated the car bomb, the second joined the first and engaged with prison guards at the front gate while the third dispersed throughout the prison, engaging with security forces outside. Other militants were firing from the rooftops of houses surrounding the prison.
Authorities suspect the attackers received help from inside the prison in order to allow the inmates to break free, one security official said. He added at least three of the prison officials and guards were detained.
They also said that authorities received information of possible attack on Interior Ministry, in charge of police, and Defense Ministry.
The official spoke on condition of anonymity because he was not authorized to speak to the media.
The ousted President Ali Abdullah Saleh's party said it fears that those who fled were involved in an attempt to assassinate him in 2011.
Abdu al-Janadi, Saleh's party spokesman said, "we are warning of helping prisoners to escape. We are waiting for a transparent investigation into the incident."
Saleh was removed from power in a yearlong uprising that started in 2011 and ended after he signed a power transfer deal that gave him immunity from prosecution in return for leaving power in 2012.
During the uprising, he came under attack in his presidential palace that left him with severe injuries requiring surgeries in neighboring Saudi Arabia.
Yemen has witnessed major jailbreaks in the past that have fueled militancy, including one in February 2006 when 21 al-Qaida militants dug a tunnel and fled the intelligence prison in Sanaa. Many of those who fled at that time are now the group's most wanted and dangerous men, including its military commander Qassim al-Raimi who is believed to have been behind a series of foiled attacks against Americans.
Three years earlier, 11 al-Qaida militants escaped during another prison break took place when 11 of al-Qaida militants fled, including the suspected perpetrators of the 2000 bombing of the USS Cole in Aden harbor that killed 17 American sailors.
Washington considers al-Qaida in the Arabian Peninsula, the group's Yemeni offshoot, its most dangerous branch. It seized large swaths of lands in the south before the military launched a major offensive in the summer of 2012, driving many of them out. The group has continued to carry out ambitious and deadly attacks, including storming the Defense Ministry headquarters leaving 56 dead last month, including foreigners.