The attackers — thought to number around six — destroyed at least two P-3C Orion maritime surveillance aircraft given to Pakistan by the US and killed 10 security officers. At least four of the attackers were killed, and two others may have escaped, said Pakistan Navy chief Nauman Bashir.

The Pakistani Taleban claimed responsibility for the assault in Karachi. The militants said it was revenge for the May 2 American raid that killed Al-Qaeda chief Osama Bin Laden.

The insurgent team armed with grenades, rockets and automatic weapons stormed Naval Station Mehran under cover of darkness late Sunday, using ladders and cutting the wire to get into the facility, Interior Minister Rehman Malik said.

Once inside, they scattered around the compound, setting off explosions and hiding in the sprawling facility.

On Monday, the militants were holed up in an office building during a gunbattle with commandos, navy spokesman Irfan ul Haq said. By the afternoon, Haq said the militants had been defeated. Commandos leaving the complex flashed victory signs to reporters.

Malik said the militants were dressed in black and looked "like the Star Wars characters."

Six Americans and 11 Chinese aviation engineers were on the base but escaped unharmed, he said. US Embassy spokesman Alberto Rodriguez said the Americans were working as contractors to help support the P-3C aircraft but did not report to the US Embassy or Consulate.

The insurgents' ability to penetrate the facility rattled a military establishment already embarrassed by the unilateral American raid on Bin Laden's hid-out and raised the possibility they had inside help.

It will also likely lead to more questions over the safety of Pakistan's nuclear weapons. In 2009, terrorists stormed army headquarters close to the capital, holding hostages for 22 hours. But unlike the attack Sunday in Karachi, the attackers then failed to deeply penetrate the complex.