Attackers in Afghan police uniforms gunned down a member of NATO's peacekeeping force in southern Afghanistan on Monday, the allied command in Kabul reported.

The International Security Assistance Force said the three gunmen "immediately fled the area and are currently being sought."

No other details were released by NATO, but a U.S. official in Washington told CNN the fatality was an American and that as many as eight or nine others were wounded.

Uniformed Afghans -- either insurgents in disguise, or members of the country's police or military -- have been behind numerous killings of U.S. and NATO troops this year. The incidents have fueled mutual distrust between Afghan and NATO forces in the now-decade-old conflict.