Updated | NATO helicopter shot down by Taliban

President Hamid Karzai's office said the helicopter crash killed 31 US special forces and seven soldiers from Afghanistan. The helicopter was shot down by a grenade launched missile.

The helicopter was taking the personnel back to their base after an operation. It is not clear how the crash happened but the Taliban said they shot the helicopter down.

The incident is believed to be the biggest single loss of life for US forces in Afghanistan since operations began in 2001.

A spokesman for the NATO-led International Security Assistance Force (ISAF) said it was still looking into what had happened and how the helicopter crashed in the eastern province of Wardak, southwest of the Kabul.

NATO said the alliance was conducting a recovery operation Saturday at the site and investigating the cause of the crash, but did not release details or a casualty figure.

"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."

However, news media report that the helicopter crashed as it was trying to take off after landing on the roof of a Taliban commander's home during a firefight, where eight insurgents were killed.

Taliban spokesman Zabiullah Mujahid said the insurgent group was responsible for shooting down the helicopter and acknowledged that eight of its fighters had been killed.