A suicide bomber disguised as a soldier has blown himself up in front of police headquarters in Afghanistan's southern Helmand province, killing himself and four policemen.

A police chief in Helmand says the bomber dressed in an Afghan army uniform detonated his explosives after police stopped him as he tried to enter the station in Lashkar Gah, the province capital. At least one other policeman was injured.

NATO forces have launched a major offensive in Helmand, Afghanistan's top opium producing region where Taleban militants have staged attacks.

NATO and Afghan forces say they have killed dozens of Taleban fighters in recent days.

In other news, U.S.-led coalition forces and Afghan troops arrested four men and seized weapons in a raid on a compound in Jalalabad in the eastern province of Nangarhar.

Some information for this report was provided by AFP, AP and Reuters.