In the first crash, seven soldiers and three American civilians died after their helicopter crashed as they were leaving a drug raid in western Afghanistan. NATO officials said more than 12 enemy fighters died in the raid.
Eleven U.S. soldiers, 14 Afghan soldiers and one U.S. civilian were also injured in that crash.
The New York Times reported that a military spokeswoman, Capt. Elizabeth Mathias, would not specify an exact location for the deadly crash in the west, although she said the military was “98 percent sure that insurgent activity was not involved.”
In a separate incident, two U.S. Marine helicopters collided in flight in the southern province of Helmand, killing four American troops and wounding two more, Marine spokesman Capt. Bill Pelletier told news agencies.
U.S. authorities have ruled out hostile fire in the midair collision incident, the Associated Press reported.
"These separate tragedies today underscore the risks our forces and our partners face every day," NATO spokesman Col. Wayne Shanks said Monday. "Each and every death is a tremendous loss for the family and friends of each service member and civilian. Our grief is compounded when we have such a significant loss on one day."
Taliban spokesman Qari Yusuf Ahmedi claimed insurgent fighters shot down a helicopter in northwest Badghis province's Darabam district, according to the AP. It was impossible for news agencies to verify the claim, and unclear if he was referring to the same incident.
This has been the deadliest year for international and U.S. forces since the start of the U.S.-led 2001 invasion of the country. Monday marked the heaviest single-day loss of life since June 28, 2005, when 16 U.S. troops died when their MH-47 Chinook helicopter was shot down by insurgents.
The deaths come as the Obama administration is weighing shifts in U.S. strategy in Afghanistan, including the possibility of sending additional troops to the region.
The top U.S. commander in the region, Gen. Stanley McChrystal, has reportedly recommended that President Barack Obama add as many as 40,000 more to battle a strengthening insurgence along the Afghan-Pakistan border.
The International Council on Security and Development, a think tank, estimates that the Taliban has a permanent presence across 80 percent of Afghanistan.
A runoff election for a new Afghan president is scheduled for Nov. 7 between current leader Hamid Karzai and his top rival, former foreign minister Abdullah Abdullah. The runoff vote comes after a United Nations report cited massive fraud in the processing of ballots from the original poll.
---- Compiled from wire reports and other media sources