(Reuters) - An overnight battle with militants at Pakistan's naval aviation base erupted again after dawn on Monday, with blasts ringing out and choppers hovering overhead as security forces launched a counter-offensive.
"The operation still continues. It is not over yet," said one security official, eight hours after a group of up to 15 militants stormed the installation with guns and grenades, killing at least five people and blowing up a military aircraft.
More than 30 troops entered the PNS Mehran base in the southern city of Karachi as the battle resumed and eight blasts were heard in the space of 30 minutes.
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.
"They were carrying guns, rocket-propelled grenades (RPG) and hand grenades. They hit the aircraft with an RPG," Navy spokesman Commander Salman Ali said earlier.
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.
The dead included one sailor, three firefighters and an Army ranger, Yasir said.
The Karachi attack evoked memories of an assault on Pakistan's army headquarters in the town of Rawalpindi in 2009, and revived concerns that even the most well-guarded installations in the country remain vulnerable to militants.
A spokesman said one P-3C Orion, a maritime patrol aircraft, had been destroyed and that intermittent gunfire was continuing.
Interior Minister Rehman Malik said earlier the militants had attacked from the rear of the base. "We have been able to confine them to one building and an operation is underway either to kill or capture them."
Media reports said the attackers had made their way in through a sewer line, but that was not confirmed. The military's goal is to capture as many of the attackers alive as possible, Pakistan television reported.
Pakistani military and paramilitary reinforcements poured in after the attack began, with four vehicles carrying about 10 troops each moving into the base.
Prime Minister Yusuf Raza Gilani condemned the attack.
"Such a cowardly act of terror could not deter the commitment of the government and people of Pakistan to fight terrorism," Gilani said in statement.
WAVE OF BOMBINGS
Pakistan has faced a wave of bombings and gun assaults over the last few years, some of them claimed by the Tehrik-e-Taliban Pakistan (TTP), or Pakistani Taliban.
Others have been blamed on al Qaeda-linked militant groups once nurtured by the Pakistani military which have since slipped out of control.
The discovery that bin Laden was living in the garrison town of Abbottabad, not far from the Pakistan Military Academy, has revived suspicions that militants may be receiving help from some people within the security establishment.
Pakistan and the United States say the senior leadership in the country did not know bin Laden was in Abbottabad.
Washington sees nuclear-armed Pakistan as a key, if troubled, ally in the region essential to its attempts to root out militant forces in neighboring Afghanistan.
"We condemn the attack and our sympathies are with the families of those injured or killed," the White House in Washington said in a statement.
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.