Liaquat Ali, a Peshawar city police chief, said that two of the wounded people were in a critical condiditon.

"The small building at the police checkpoint was destroyed. A nearby house and a mosque were also damaged," he said.

The northwestern region is at the forefront of Pakistan's battle against Taliban, al-Qaeda and other opposition groups who launch attacks from the tribal mountainous area both within Pakistan and bordering Afghanistan.

US drones - unmanned aircraft - also carry out missions against these fighters in the region.

The Pakistani military have increased attempts to gain control of the northwest over the last year, launching major offensives and killing hundreds of opposition fighters.

But opposition groups have continued to function, carrying out about 50 bomb attacks in the last year, killing about 500 people.