4 US soldiers die in Afghan chopper collision

The US military says four American troops have been killed and two injured in a midair collision of two helicopters in southern

Afghanistan.

Hostile fire has been ruled out in the crash, which occurred on Monday morning. No further details were released.

In an unrelated incident, another helicopter went down Monday during a joint, international security force operation against insurgents in western Afghanistan in which a dozen militants were killed.

The US said military casualties were reported and a recovery operation is under way.

At least 14 Americans have been killed in a series of air crashes in Afghanistan, military officials say.

In the first incident, four US soldiers died and two were hurt when two helicopters collided mid-air in the south, Nato-led forces said.

In a separate incident seven soldiers and three civilians were killed in a helicopter crash in the west.

Hostile fire was ruled out as a cause of the collision but no cause has yet been identified for the crash.

Twelve Americans and 14 Afghans were injured in that incident.

This year has seen the highest death toll of international troops in Afghanistan since the Taliban were overthrown in 2001.

There have been dozens of American soldiers among those killed.