President Hamid Karzai sent his condolences to President Barack Obama, according to a statement issued by his office.
"A NATO helicopter crashed last night in Wardak province," Karzai said in the statement, adding that 31 American special operations troops were killed. "President Karzai expressed his deep condolences because of this incident and expressed his sympathy to Barack Obama."
NATO confirmed the overnight crash and said the alliance was conducting a recovery operation at the site and investigating the cause of the crash, but did not release details or a casualty figure. The coalition said there "was enemy activity in the area."
"We are aware of an incident involving a helicopter in eastern Afghanistan," said U.S. Air Force Capt. Justin Brockhoff, a NATO spokesman. "We are in the process of accessing the facts."
A spokesman for Wardak province, Shahidullah Shahid, said the helicopter crashed in the Sayd Abad district of Wardak province. The volatile region borders the province of Kabul where the Afghan capital is located and is known for its strong Taliban presence.
Taliban spokesman Zabiullah Mujahid claimed the downed aircraft was a U.S. military helicopter and that the Taliban fighters had brought it down with a rocket attack.
In a written statement released Saturday, Mujahid said that NATO attacked a house in Sayd Abad where insurgent fighters were gathering Friday night.
Mujahid said the Taliban fired on NATO and downed the helicopter, killing all the crew. He said eight insurgents also died.
in June 2005, 16 American troops were killed when a U.S. helicopter crashed in eastern Kunar province after apparently being hit by a rocket-propelled grenade.
At NATO headquarters in Brussels, an official said it was a twin-rotor Chinook helicopter. The official, who spoke on condition of anonymity, said he was receiving his information from an Afghan officer in Kabul.