KABUL - Two helicopter crashes in Afghanistan killed 11 U.S. soldiers and three U.S. civilians on Monday, NATO-led forces said in a statement.

Neither crash was caused by hostile fire, NATO said.

This year has seen a surge of violence in Afghanistan as an increasingly fierce Taliban step up operations against U.S. and NATO forces operating in the country.

Seven U.S. service members and three U.S. civilians were killed when a NATO helicopter crashed in western Afghanistan following an operation against insurgents in which a dozen Taliban fighters were killed.

Eleven U.S. troops, 14 Afghan soldiers and a U.S. civilian were injured in the crash.

Four U.S. service members were killed and two were injured when two helicopters operated by NATO-led troops collided in mid-air in southern Afghanistan, NATO said in an earlier statement.

On Saturday in eastern Afghanistan, one U.S. soldier was killed in a roadside bomb attack and another died of wounds from an insurgent attack, NATO said in a statement on Monday.

A spokeswoman for ISAF, the International Security Assistance Force, could not give any further information on the casualties or the exact location of the crashes.

(Writing by Golnar Motevalli; Editing by Nick Macfie)

Afghanistan