Afghan officials say an Afghan security officer opened fire on U.S.
troops while conducting a joint operation with them, killing two and
wounding two others.
A spokesman for the governor of Wardak province said the shooting occurred late Friday while Afghan and U.S. forces were on patrol together in Wardak.
It is unclear what motivated the shooting.
A statement from NATO-led forces in Afghanistan said two U.S. soldiers died from injuries sustained in a "hostile attack" Friday, but declined to give further details.
NATO says two other U.S. troops died Friday in a bomb attack in southern Afghanistan. Another died of wounds sustained in a bomb attack in eastern Afghanistan.
U.S. and NATO troops in Afghanistan have recently been facing stiffer Taliban resistance.
2009 is the deadliest year for foreign forces since the conflict began nearly eight years ago.
Some information for this report was provided by AP and Reuters.