A helicopter was shot down in Afghanistan last night, and authorities say 31 U.S. troops and seven Afghan commandos were killed. AP reports that more than 20 Navy SEALs from Team Six, the unit that killed Osama bin Laden, were among those who died in the crash. Officials believe it was the deadliest single attack for American forces in the decade-long war.

"A NATO helicopter crashed last night in Wardak province...President Karzai expressed his deep condolences because of this incident and expressed his sympathy to Barack Obama," said a statement from the office of President Hamid Karzai.

The Taliban have taken credit for the attack, saying they shot it with rocket fire while it was taking part in a raid on a house where insurgents were gathered. NATO confirmed that there “was enemy activity in the area” at the time of the attack, but added, “We are in the process of accessing the facts."

One source told AP that the team was thought to include 22 SEALs, three Air Force air controllers, seven Afghan Army troops, a dog and his handler, and a civilian interpreter, plus the helicopter crew. The source added that this was the largest single loss of life ever for SEAL Team Six, known as the Naval Special Warfare Development Group. The incident will eclipse the single deadliest attack for American troops in Afghanistan, which came in June 2005, when 16 American troops were killed when a U.S. helicopter crashed in eastern Kunar province after apparently being hit by a rocket-propelled grenade.