A NATO chinook helicopter was shot down in Afghanistan during an overnight operation in eastern Afghanistan, the New York Times reports, killing at least 37 people on board. At least 31 U.S. soldiers were killed, as well as seven Afghan soldiers, a statement from the Afghan president's office said. If confirmed, this would be the deadliest day for the U.S. since the start of the war.

This is what happened, as far as we know: The helicopter was hit by a rocket-propelled grenade in the Tangi Valley of the Wardak Province just west of Kabul. According to Al-Jazeera, the Taliban "quickly claimed to have shot down the helicopter during a firefight." They also said eight of their fighters were killed in the fighting. A spokesman for the Taliban, Zabiullah Mujahid, said insurgents shot down the helicopter around 11 p.m. Friday as it was starting an operation on a house where the militants were gathering, the Times reports. Sources on the ground also told Al Jazeera "that the helicopter was apparently taking off from a roof of a building during this operation when it then crashed."

However, reports are conflicting. Gen. Abdul Qayum Baqizoy, police chief of Wardak, said the operation began around 1 a.m. Saturday as NATO and Afghan forces attacked a Taliban compound, and the firefight lasted at least two hours. Reports are also unconfirmed as to the nationality of the NATO soldiers killed, but the Times notes that "Americans were known to be carrying out most of the operations in the area." But if confirmed, the U.S. casualties would outnumber those in June 2005, the second most deadly day, where 16 U.S. troops were killed when their helicopter crashed in eastern Kunar province after apparently being hit by a rocket-propelled grenade.

ABC News also reports on the victims:

Initial reports indicate up to 25 Navy SEALs were on the aircraft at the time.

It was also carrying seven Afghan Special Forces troops, one interpreter, five member helicopter crew and one dog.

Update: Latest reports on Twitter indicate that: "WASHINGTON (AP) - AP sources: Majority of those killed in helicopter crash were from Navy SEAL Team 6." Another report from the AP says the team contained "22 SEALs, three Air Force air controllers, seven Afghan Army troops, a dog and his handler, and a civilian interpreter, plus the helicopter crew."

Update: Now the AP reports that "that none of the Navy SEALs who died in a helicopter crash in Afghanistan had participated in the raid that killed Osama bin Laden, although they were from the same unit that carried out the bin Laden mission." Additionally, ABC News Senior Foreign Affairs Correspondent Martha Raddatz tweets that: "There are only about 2000 SEALS. Losing more than 20 is unbearable."

CNN reports that Afghan President Hamid Karzai issued a statement offering "deep regret" to President Barack Obama. Obama in turn issued a statement saying: "My thoughts and prayers go out to the families and loved ones of the Americans who were lost earlier today in Afghanistan. We also mourn the Afghans who died alongside our troops in pursuit of a more peaceful and hopeful future for their country."