Karachi: Pakistani security forces on Monday ended a 15-hour siege of a key naval base that terrorists stormed overnight, sparking fierce battles that left 16 people dead, officials said. The dead included 12 security personnel and four of the attackers who exploded themselves at PNS Mehran naval base in one of the worst and most aduacious of terror attacks in Pakistan in recent times.

Four terrorists were arrested, media reports said. The attack targeted P-3C Orion aircraft, two of which were destroyed.

The terrorists reportedly took hostage a number of people, including Chinese military personnel. Their fate was not immediately known.

A large number of terrorists, their number estimated between 10 and 25, stormed the base Sunday night, Xinhua reported citing local media reports. They were armed with automatic weapons, rocket launchers and grenades.

The mayhem began in no time as the armed men scattered in the complex with one aim: kill and destroy.

Over 20 bomb explosions quickly shook the otherwise heavily-guarded naval facility on Sunday night.

Four equally powerful blasts were also heard at the nearby air force base. Television footage showed thick smoke billowing from the area.

Fierce gunfights raged through the night as reinforcements of security forces rushed to the base.

The Pakistani Taliban, which is opposed to Islamabad's pro-US policies, reportedly claimed responsibility for the attack, Xinhua said.

At one point, the terrorist retreated into a building within the base holding hostages as human shield to fight back the navy commandos, Rangers and security personnel.

Pakistani commandos supported by helicopters battled the terrorists. Four militants who had camouflaged themselves in dark outfits were arrested, media reported.

After 15 hours of intermittent fighting, the security forces managed to regain control of the complex, BBC reported.

A police official said 12 security personnel were killed. The terror attack comes within three weeks of Al Qaeda leader Osama bin Laden's killing May 2 in Abbottabad by US commandos. The Taliban had vowed retaliation.

Earlier reports said four foreigners were killed. They were believed to be US engineers working at the air force base.

But a spokesperson from the US consulate denied the report. It was the third militant attack on the navy in Karachi in a month.

At least five people were killed and 18 injured in a bombing of a Pakistan Navy bus here April 28, two days after twin blasts blew up two naval buses killing four people.

Prime Minister Yousuf Raza Gilani has condemned the attack.