Updated

Heavily armed militants attacked Yemen's main prison in central Sanaa on Thursday, killing seven people and helping a number of inmates to escape, the country's state agency reported.

The attack started with a car bomb, then militants exchanged 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.

The news agency didn't say how many inmates fled or what charges they were faced. It added that authorities are investigating.

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 is on the main road leading to the airport, which was closed.

Authorities suspect the attackers received help from inside the prison in order to allow the inmates to break free, a security official said on condition of anonymity because he was not authorized to speak to the media.

Yemen has witnessed major jailbreaks in the past, including one in February 2006 when 21 Al Qaeda 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 Qaeda militants escaped during another prison break took place when 11 of Al Qaeda militants fled, including the suspected perpetrators of the 2000 bombing of the USS Cole in Aden harbor that killed 17 American sailors.

Al Qaeda's Yemeni offshoot known as Al Qaeda in the Arabian Peninsula has carried out a series of attacks in a bid to fight back against a government offensive aimed at uprooting it from strongholds in the south.