Six police officers were killed on Sunday in a car bomb attack on their headquarters in the southern Afghan city of Kandahar, a bastion of Taliban militancy, a local government official said.

The blast, which happened in the car park, wounded 19 others -- six police and 13 civilians -- provincial government spokesman Zulmai Ayobi told AFP. It was not immediately clear if the explosion was a suicide attack.

Kandahar is the largest city in southern Afghanistan and the birthplace of the Taliban, who have been fighting for a return to power since being ousted by the US-led invasion in late 2001 that followed the 9/11 attacks.

Militants frequently target Afghan police and military, who are due to take responsibility for the country's security from NATO troops by the end of 2014.

A UN report on Saturday said civilian deaths in Afghanistan reached a record high in 2011 -- the fifth straight year the death toll has gone up.