KANDAHAR: A powerful explosion wounded six people on Saturday outside police headquarters in Kandahar city, one of the focal points of the fight against the Taliban, officials said.

Helmand and Kandahar provinces have been the epicentre of a renewed surge against Taliban militants by US and other foreign troops over the past 18 months.

Commanders say some areas, like Kandahar city, have largely been brought under control but violence still rages across wide areas of the south.

Violence is at its worst across Afghanistan since the Taliban were ousted by US-backed Afghan forces in late 2001, a worrying sign as US President Barack Obama this week reviews his war strategy before a gradual troop drawdown begins from July 2011.

Zalmai Ayoubi, a spokesman for the Kandahar governor, said four police and two civilians had been wounded in the blast.

A bomb had gone off inside a vehicle in a deserted area near Kandahar police headquarters which has been turned into a parking lot for police vehicles, Ayoubi and other police said.

It was not clear whether the bomb had been detonated remotely or whether it had been a suicide attack, they said.

Four police vehicles were destroyed and windows were shattered in the police headquarters, as well as in a nearby Information and Culture Ministry building, they said.

A Reuters witness said smoke and dust could be seen rising above the building but roads to the area had been blocked.