NATO says three of its troops and an Afghan soldier are dead after two separate clashes with Taleban insurgents in Afghanistan.

Two NATO soldiers along with an Afghan soldier were killed Friday while fighting insurgents in the eastern province of Nuristan. Thirteen other NATO troops were wounded, as well as an Afghan soldier and a civilian.

The third NATO soldier was killed in southern Afghanistan.

NATO has not revealed nationalities of the dead soldiers.

The British Ministry of Defense announced Saturday that one of its soldier was killed in a rocket attack in Afghanistan's southern Helmand province Friday.

Violence has surged in Afghanistan during the past 18 months - the bloodiest period since U.S.-led troops overthrew the Taleban in 2001.

NATO officials say one of its attack helicopters was forced to make a controlled landing in eastern Afghanistan Friday because of engine failure. The helicopter was supporting the evacuation of wounded NATO troops when it was forced to land.

The cause of the engine failure is not known, but NATO says insurgent activity was reported in the vicinity.

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