Rocket-propelled grenades (RPGs) and automatic rifles were fired at police during a patrol in the southern province of Helmand late on Sunday, said a spokesman for the local government official.
The attack occurred not far from a district in neighbouring Kandahar province where five police officers were killed in a similar raid earlier this month.
Officials blamed the attack on remnants of the ousted Taliban and al-Qaeda members.
The raid followed reports from a Taliban official that the group’s elusive leader Mullah Mohammad Omar had appointed a new deputy commander for the south on Saturday and ordered him to intensify attacks on US and government forces.
US-backed Afghan police and the fledgling national army have been regular targets since American-led troops ousted the Taliban in October 2001.
In the southeast of the country US and Afghan forces arrested seven Taliban suspects. A US military spokesman said they had seized several arms caches containing rocket explosives, mortar bombs and small-arms ammunition.
11,500 US-led forces remain in war-torn Afghanistan in an effort to stamp out remaining members of the Taliban and al-Qaeda.