Men wearing Afghan police uniforms shot dead two NATO service members Saturday in southern Afghanistan, authorities said, the latest in a string of attacks on international troops by Afghan security forces or militants disguised as police.

Two other coalition service members also died Saturday in Afghanistan, one in an insurgent attack and another of non-battle related injuries.

There were conflicting reports about the shooting in Helmand province.

Fareed Ahmad, a spokesman for the Helmand provincial police, said two Afghan policemen opened fire on coalition troops at 3 p.m. at a joint Afghan-coalition compound, killing two coalition troops. He said a third Afghan policemen fired at the attackers, killing one and wounding the other, who escaped.

The attackers had been members of the Afghan National Police for one year and were from Nangarhar province in eastern Afghanistan, according to Ahmad