A helicopter crash in Afghanistan's eastern Wardak province killed 31 US special operation troops and seven Afghan soldiers, the country's president said Saturday.
It was the highest number of American casualties recorded in a single incident in the decade-long war.
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.
The Taliban claimed to have brought the helicopter down with a rocket attack, but they have been known to make exaggerated claims in the past.
NATO confirmed the overnight crash and said there "was enemy activity in the area."
But it said it was still investigating the cause.