Source / Courtesy: BBC
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.
The helicopter went down overnight in Wardak province, the statement from President Karzai’s office said.
It was returning from an operation against the Taliban in which eight insurgents are believed to have been killed.