"We arrested some 48 policemen for their unlawful actions on Monday, but 12 others handed themselves over to the Taliban," provincial deputy governor Mohammad Younis Rasooli said.

"We are investigating the arrested policemen to find out what other crimes they have committed," Rasooli said.

The police, often the only arm of the Afghan state active in isolated outposts across the mountainous country, suffer more casualties than any other force.

Non-existent before 2001, as Afghanistan had no concept of a national police, the force has been criticised for endemic corruption, and become renowned for fleeing in the face of Taliban attacks and milking the populace for bribes.

On Monday a Taliban spokesman said that about 35 Afghan police had defected to the Islamist group.

More than seven years since US-led and Afghan troops toppled the Taliban after the September 11 attacks in the United States, violence against civilians and foreign troops has increased in Afghanistan.

The Taliban, who have vowed to drive out about 65,000 foreign troops deployed by NATO and the US military, are gaining ground, particularly in the south.