Four U.S. troops were on board a Black Hawk helicopter when it crashed Thursday in Helmand province in southern Afghanistan, a military official said.
The number of casualties and the cause of the crash were not immediately clear, said the officer.
"There was bad weather occurring at the time of the crash, but enemy action cannot be ruled out at this time," said the officer, who is based in Kabul.
Last year, a military helicopter was shot down in eastern Afghanistan, killing 38 U.S. and Afghan troops, including 17 who were part of the Navy SEALs unit that killed Osama bin Laden May 2 in Pakistan. In January, a helicopter accident killed six members of the international military force in Afghanistan.
Meanwhile, Afghan President Hamid Karzai suggested Thursday that a speeded-up departure of Western troops is the only way to prevent a recurrence of "painful experiences" such as the sight of American soldiers posing with the body parts of dead insurgents.
In a statement issued by the Afghan presidential palace 24 hours after the Los Angeles Times published photos showing U.S. troops with the remains of suicide bombers and mugging for the camera, Karzai called the behavior depicted "inhumane and provocative."
"It is such a disgusting act to take photos with body parts and then share it with others," he said.
The Taliban, in its first public statement since the pictures of U.S. soldiers and dead bombers appeared, denounced the "gruesome acts" depicted in the photos. The militant group also lambasted Afghan soldiers who were present in some of the shots.
"Some Afghan hirelings posed in the photos, at their masters' orders, to scorn the remains of martyrs," the statement said.
The Obama administration has condemned the actions shown in the photos, and the U.S. military has launched an investigation of the incidents, which took place in 2010.
The palace statement said Karzai has sought an "accelerated and full transition of security responsibilities to Afghan forces, so Afghanistan can take over its own destiny, and thus no such things can be repeated by the foreign forces in Afghanistan."
The NATO force is to wind down its combat role by the end of 2014, but growing numbers of troop-contributing nations have indicated they will pull out their forces next year.
The transfer of security responsibilities to Afghan forces, which has been in progress for a year, is a key prelude to the exit of Western combat troops.