Two members of the security forces and at least 15 insurgents were killed in a four-hour gunbattle that erupted following two successive attacks on the security post set up to defend Peshawar, the gateway to the troubled northwest region.

"They were well-armed. They had heavy weapons, rockets, mortars everything. The fighting lasted for about four and a half hours," Ejaz Khan, a city police officer, said.

The attack took place near Khyber, part of Pakistan's lawless tribal belt on the Afghan border, which is regarded as a global hub of militants, including al Qaeda and the Pakistani and Afghan Taliban movements.

Two members of the security forces were killed and five wounded, Khan said. At least 15 insurgents were killed.

Security forces repulsed the first attack by the militants which was carried out just before midnight, officials said.

"Then they carried out a big attack early in the morning. We also called in reinforcements to counter the attack and we did it," a Peshawar security official said.

There was no immediate claim of responsibility, but militants linked to al Qaeda and the Taliban have stepped up attacks in Pakistan after the killing of bin Laden in A military town by U.S. special forces on May 2.

The Pakistani Taliban, who are close to al Qaeda, have vowed to avenge bin Laden's death and said their suicide bombers killed 80 people last week at a paramilitary academy in the northwestern town of Charsadda.

In a suspected sectarian attack on Wednesday, two men on a motorbike fired on a vehicle and killed four Shi'ite Muslims and wounded four others on the outskirts of the southwestern city of Quetta.

Pro-Taliban Sunni militants groups, many of whom are linked to al Qaeda, are trying to foment conflict among Pakistan's religious sects in an attempt to destabilize the government just as it faces pressure from the United States and the West to crack down on militant groups, analysts say.

Pakistan has come under renewed pressure to prove it is serious about tackling militancy since bin Laden was discovered after apparently spending at least five years in the South Asian nation about a two hour drive from the headquarters of the country's intelligence service.