4 U.S. troops die as copters collide in south Afghanistan

Four American troops were killed and two injured today when two helicopters collided in southern Afghanistan.

Hostile fire has been ruled out in the crash, the military said in statement. U.S. military spokesman Col. Wayne Shanks said he did not yet have other details.

In an unrelated incident, another helicopter went down today during an operation against insurgents in western Afghanistan. A dozen militants were killed, authorities said.

The U.S. said that military casualties had been reported and a recovery operation was underway. Casualties can refer to either dead or injured.

This has been the deadliest year for coalition forces since the 2001 invasion. Fighting spiked around the presidential vote in August, and 51 U.S. soldiers died that month -- the deadliest for American forces in the eight-year war.

So far in October, 34 American troops have died, according to icasualties.org.