Nine explosions were reported from the PNS Mehran base in the southern city of Karachi after the late-night assault by up to 15 gunmen, who targeted three hangars housing aircraft.

"They were carrying guns, rocket-propelled grenades (RPG) and hand grenades. They hit the aircraft with an RPG," said Navy spokesman Commander Salman Ali. "They are still inside the base."

Eleven people were wounded in the attack on one of the country's most heavily guarded military installations, where jet fuel tanks appeared to have caught fire and exploded.

It was not immediately clear who was behind the raid. But Taliban militants, who have vowed to avenge the killing of Osama bin Laden by U.S. special forces, have carried out several attacks since the al Qaeda leaders' death on May 2.

The assault started at approximately 10:30 p.m. on Sunday and it took about four hours before most of the fires were extinguished and the shooting had abated. Security forces then swept the base in search of the assailants.

On April 28, suspected militants detonated a roadside bomb in Karachi, killing four members of the navy, the third attack on the navy in a week.

The attack came two days after two bombs hit buses carrying navy personnel, killing four people and wounding 56. Taliban insurgents took responsibility for the twin attacks.