A Taliban suicide bomber flattened a Pakistani police station on Wednesday, killing six people in the latest brazen assault on security forces since US troops killed Osama bin Laden.

The dawn truck bombing brought down the three-storey building in the military zone of the northwestern city of Peshawar, not far from the US consulate, just days after an American diplomatic convoy was attacked.

The country’s main Taliban faction claimed responsibility for the attack, saying it was their fourth reprisal for the May 2 death of bin Laden, whose discovery and killing in Pakistan humiliated the military and government.

The Peshawar bombing will likely highlight doubts about the security forces’ ability to protect not only themselves but major cities, and fuel a long-running debate about the security of the country’s nuclear weapons.

Five policemen and a soldier died in Wednesday’s explosion, a relatively low toll given the enormity of the blast, but officials said the building normally had only a skeleton staff at the time of the attack shortly before 5:00 am.

An AFP reporter saw flames from the stricken building, shattered glass on the ground, pancaked rubble, burning tyres and the charred remains of at least three vehicles, including a small truck.

Constable Farid Khan, who had his shoulder fractured in the attack and was admitted to a hospital, told AFP that he was saying his morning prayers inside the police station when a deafening explosion took place.

"The roof of the building collapsed," he said, adding that he had been pinned down because of his injury until his colleagues took him to hospital.

"It was a huge blast which completely destroyed the three-storey building," police official Muhammad Ijaz said.

Another police official, Shafiullah Khan, said six people died and rescuers were looking for up to three people still trapped under the rubble, with 36 already taken to hospital with injuries.

"An estimated two to three people are still feared to be trapped under the rubble. Rescuers are trying to pull them out. I hope we take them out alive," Khan said.

Peshawar is the gateway to Pakistan’s northwestern tribal belt on the Afghan border, where US drone strikes routinely target Taliban and Al-Qaeda operatives.

The razed building housed the police Criminal Investigation Department and was located in the Peshawar Cantonment area just 150 metres (yards) from the US consulate. The area houses military families and security is normally tight.

Police said the attack was carried out with a small truck containing at least 200-250 kilograms (440-550 pounds) of explosives, and that body parts were hurled more than 300 metres (yards) away from the blast.

"We will further step up these attacks to avenge Osama bin Laden’s martyrdom," Taliban spokesman Ehsanullah Ehsan told AFP by telephone from an undisclosed location.

"These attacks will continue until the US drone strikes and ongoing Pakistani military operations are stopped in the tribal regions," he added.

Last Friday, the Taliban bombed a US consulate convoy in Peshawar, killing one Pakistani and wounding 11 other people in the first attack on Americans in Pakistan since bin Laden’s killing in the town of Abbottabad.

Late on Sunday, heavily armed Taliban gunmen stormed a naval base in Pakistan’s biggest city Karachi, destroying two US-made surveillance planes and killing 10 personnel in a 17-hour standoff.

That was the worst assault on a military base since the army headquarters was besieged in October 2009, and piled further embarrassment on the armed forces three weeks after bin Laden was found living under their noses.

Bin Laden was killed by US commandos in Abbottabad, a garrison town north of Islamabad, prompting fierce controversy about whether Pakistan’s security establishment was complicit in hiding the Al-Qaeda leader or plain incompetent.

Following the brazen attack in Karachi, NATO chief Anders Fogh Rasmussen said Tuesday in Kabul that he was confident Pakistan’s nuclear weapons were safe, but admitted the issue was a "matter of concern".

Militant unrest, much of it in the form of suicide attacks, has killed nearly 4,400 people in the past four years as the Taliban and militants linked to Al-Qaeda wage a bloody onslaught on Pakistan’s US-allied leadership.