The Taliban claimed they downed the helicopter with rocket fire while it was taking part in a raid on a house where insurgents were gathered in the Province of Wardak late Friday. It said wreckage of the craft was strewn at the scene.
U.S. officials confirmed to NBC News that the U.S. believes the helicopter was shot down. One senior defense official, speaking on condition of anonymity, said the military does "not have any indication that it was anything other than" hostile fire.
NATO confirmed the overnight crash took place and that there "was enemy activity in the area." But it said it was still investigating the cause and conducting a recovery operation at the site. It did not release details or casualty figures.
One current and one former U.S. official said that the dead included more than 20 Navy SEALs from SEAL Team Six, the unit that carried out the raid in Pakistan in May that killed bin Laden. They were being flown by a crew of the 160th Special Operations Aviation Regiment. Both officials spoke on condition of anonymity because families are still being notified.
None of those killed in the crash is believed to have been part of the SEALs mission that killed bin Laden, but they were from the same unit as the bin Laden team.
The death toll would surpass the worst single day loss of life for the U.S.-led coalition in Afghanistan since the war began in 2001 - the June 28, 2005 downing of a military helicopter in eastern Kunar Province. In that incident, 16 Navy SEALs and Army special operations troops were killed when their craft was shot down while on a mission to rescue four SEALs under attack by the Taliban. Three of the SEALs being rescued were also killed and the fourth wounded. It was the highest one-day death toll for the Navy Special Warfare personnel since World War II.
Source: Associated Press; NBC