An attack by a suicide bomber has killed more than 10 people, including seven policemen, in northwest Pakistan, on the border with Afghanistan, officials say.

The blast destroyed the vehicle the police were in as it drove on Wednesday through the Wazirdand area of Khyber, the district that straddles a main supply line for Nato troops in Afghanistan.

"The death toll has risen to 13. Seven are khasadar (tribal policemen) and we are trying to ascertain the identity of six others," Shafeerullah Wazir, the administration chief of Khyber, told the AFP news agency.

Rehan Gul Khattak, a local official, also gave a death toll of 13.

Wazirdand is a small town on the edge of the tribal belt which lies outside direct government control and has been branded by US officials as the headquarters of al-Qaeda.

There has been no claim of responsibility for the attack.

On Friday, at least 33 people were killed in bomb attacks targeting a bus of Shia Muslim mourners as well as the hospital where the victims were rushed for treatment in Karachi, Pakistan's biggest city.

The Pakistani Taliban and al-Qaeda-linked fighters have been blamed by officials for the deaths of up to 3,000 people in bomb attacks across the country since July 2007.