The bomber, wearing an explosives vest, apparently walked up to the gathering in Khogyani district before detonating his device, police said.

Tora Bora role

Haji Zaman was a local commander in the Tora Bora mountains when US forces launched an operation to capture or kill Osama bin Laden, the al-Qaeda leader, as he attempted to flee after the fall of the Taliban in 2001.

"Around that time Haji Zaman was at first the core commander and then the police chief in that area, he was alongside the Americans when they staged that failed operation," Bays said.

"After that, there were suspicions that he may have helped al-Qaeda escape Tora Bora and he was sent by Hamid Karzai's government into exile. He spent a lot of time in exile in Pakistan.

"It was only last year at the presidential elections, as Hamid Karzai was trying to get support from all kinds of different groups in Afghanistan, that Haji Zaman was invited back."

A number of civilians were also reported to be among the dead in the suicide blast.

The blast comes as a joint Afghan, Nato and US force battles Taliban fighters in Marjah, in southern Helmand province, in a major offensive.