A suicide car bomb targeting police killed at least nine people and wounded 31 others in a troubled northwestern Pakistani town on Thursday, police said.

"The bomber ... blew himself up when a police patrol went close to the car for a security check in Hangu town," senior local police official Abdul Rasheed told AFP.

"Nine people including three policemen were martyred and 31 wounded in the attack, which targeted the police. The injured include 12 women and four children."

Rasheed said the bomber was carrying some 300 kilograms (660 pounds) of explosives in his vehicle which he blew up in the middle of a densely populated area of Hangu, which lies some 150 kilometres (90 miles) south of Peshawar.

He added that 13 houses and shops collapsed from the impact of the blast.

Police spokesman Fazal Naeem also confirmed the attack and casualties, adding that "the blast created a 10-foot deep and 15-foot wide crater."

Prime Minister Yousuf Raza Gilani strongly condemned the attack and "deplored the loss of lives and declared it an inhuman act", an official statement said.

Local grocer Abdul Rashid, who sustained bruises to his face and shoulder after being knocked off his feet by the blast, told AFP by telephone from a hospital in Hangu that he was standing in front of his shop when the attack took place.

"I saw a blue-coloured vehicle coming close to a policemen and blowing up," he said, adding "I fell at least two metres away from my shop because of the very huge impact of the blast."

Hangu has a history of sectarian clashes between Pakistan's majority Sunni Muslims and the minority Shiites and is located near the lawless tribal belt.

The area borders the deeply conservative tribal region of Kurram, a lawless region on the Afghan border where entrenched militants oppose jobs and education for women.

Taliban and Al-Qaeda-linked militants attack daily across northwest Pakistan and the border tribal belt that Washington has branded the most dangerous place on Earth.

The United States wants Pakistan's army to do more to combat extremists on the border, including by launching a ground offensive in the district of North Waziristan, where it says key Taliban leaders reside.

The army has stalled on a ground operation, saying its troops are overstretched.

The Taliban are engaged in a campaign of violence against security forces in Pakistan, a key ally in the US-led "war against terror", claiming many attacks in revenge for US drone strikes on the rugged tribal areas.

The United States does not officially confirm the controversial missile strikes, which take place with Islamabad's tacit approval.

More than 4,000 have died in suicide and bomb attacks across Pakistan since government forces launched an attack against militants in a mosque in Islamabad in 2007.

The bombings have been blamed on terror networks linked to the Taliban and Al-Qaeda.