Yemen blamed al Qaeda for an attack in which gunmen in military uniforms raided a police headquarters in the port city of Aden on Saturday, killing 11 people and freeing several detainees.

Yemen is struggling to curb a separatist movement in the south and cement a ceasefire with Shi'ite rebels in the north.

It is under international pressure to quell domestic conflicts to focus on a growing al Qaeda presence in the country.

Saturday's attack came a day after al Qaeda's Yemen-based regional branch threatened to respond to a state crackdown against it in eastern Yemen, calling on local tribesmen to take up arms against the government.

The attack 'bore the hallmarks of al Qaeda', Yemen's Supreme Security Committee said in a statement, adding that seven security officers, three women and a seven-year-old child were killed in the early-morning assault.

Firing automatic weapons and mortars, the attackers managed to enter the intelligence police headquarters, surprising security forces there during a flag ceremony, a security official told Reuters earlier.

'The high number of casualties was due to the fact that the attack came during the morning flag salute,' the official said, adding that 'some detainees' were freed by attackers.

There was a heavy exchange of gunfire for more than an hour, and flames raged through part of the building, located near the state television headquarters in the southern seaport.

Police set up checkpoints across Aden after the attack.

'A number of suspects have been arrested,' the security official said, declining to give details.

Yemen leapt to the forefront of Western security concerns after the regional al Qaeda wing claimed responsibility for a failed attempt to bomb a U.S.-bound airliner in December.

A military operation of shelling and gunfights, launched in the eastern province of Maarib last week, sought to catch suspected Al Qaeda gunmen believed to be behind the ambush of a Yemeni military convoy that left a commander and a soldier dead. – Reuters