Around 15-20 gunmen struck PNS Mehran, the naval air station within Faisal airbase, at about 10.40 pm last night, lobbying grenades and firing indiscriminately with automatic weapons that triggered gun battles with security forces.
Fifteen loud explosions were heard from the base, the headquarters of Pakistan's naval air arm, following the attack and intermittent firing was reported till this morning.
Tehreek-e-Taliban Pakistan, which has stepped up attacks on security installations since the May 2 death of bin Laden, has claimed responsibility for the assault.
"We had already warned after Osama's martyrdom that we will carry out even bigger attacks," Taliban spokesman Ehsanullah Ehsan told foreign agencies from an undisclosed location in northwest Pakistan.
He said the attackers sent into PNS Mehran naval base had enough supplies to survive a three-day siege.
Interior Minister Rehman Malik, who was dispatched to Karachi by Prime Minister Yousuf Raza Gilani to monitor the situation, said the terrorists entered the airbase from three directions.
"A building in the premises is still under their control from where they are exchanging fire with soldiers. The situation is being tackled delicately to secure assets, minimise human losses and defeat the terrorists completely," he said.
Adding, "It is not just an attack on a navy establishment, it is an attack on Pakistan." Naval spokesman Irfan-ul-Haq told the media that four naval personnel, including an officer, and a paramilitary trooper were killed and nine more naval personnel injured in running gun battles with the terrorists.
State-run PTV said there were unconfirmed reports that four to five terrorists had been killed or captured.
"They were carrying guns, rocket-propelled grenades (RPG) and hand grenades. They hit the aircraft with an RPG," another Navy spokesman Commander Salman Ali said.
"They have destroyed two P-3c Orion aircraft," he said. The long-range reconnaissance aircraft were bought from the US by Pakistan.
Hundreds of security personnel, including from the paramilitary Pakistan Rangers and elite naval and army commandos, moved into the airbase to flush out the terrorists. Authorities used helicopters throughout the night to mount surveillance over the airbase.