According to military officials, seven American soldiers and three civilians were killed in a helicopter crash Monday in western Afghanistan.
A coalition spokeswoman, Capt. Elizabeth Mathias, would not specify an exact location for the crash, although she said the craft was a large Chinook helicopter and the military was "98 percent sure that insurgent activity was not involved."
There were 26 injuries in the crash — 14 Afghan soldiers, 11 U.S. troopers and an American civilian.
In another crash on Monday, a midair collision between two coalition helicopters in southern Afghanistan, four American soldiers were killed, Captain Mathias said, adding that gunfire from insurgents was not to blame.
Both incidents, she said, were being investigate, The New York Times reports.
It was also reported, 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.
Hostile fire was ruled out as a cause of the collision, in which another 12 Americans and 14 Afghans were injured.
No cause has yet been identified for the mid-air collision.
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, BBC News reports.
In the meantime, the Obama administration has been re-evaluating its strategy amid falling public support for the conflict and a request by the US commanding officer in Afghanistan, General Stanley McChrystal, for tens of thousands more troops.
The chairman of the joint chiefs of staff, Admiral Mike Mullen, oversaw a secret war game this month to evaluate two of the leading military options being assessed by the White House.
McChrystal has warned of possible "mission failure" unless more Nato forces are deployed immediately and new tactics are adapted to win local support.
The White House has said it is awaiting the outcome of the presidential run-off between incumbent Hamid Karzai and challenger Abdullah Abdullah before making any decision on troop numbers. It has been the deadliest year for international and US forces since the 2001 invasion to oust the Taliban. More than 30 US troops have died so far this month, guardian.co.uk reports.