The actions "appear to have been conducted by a small group of U.S. individuals, who apparently are no longer serving in Afghanistan," the International Security Assistance Force said. The statement did not identify the personnel or explain why the ISAF thought they had left the country.
A spokesman at Camp Lejeune in North Carolina would not confirm reports that the Marines were based there. "We have had elements of that unit that have deployed to Afghanistan and have returned. However, we have not yet confirmed if anyone in the video is from that unit, or whether they are attached to a unit from Lejeune," said Capt. Scott Sasser.
Pentagon officials said the criminal investigation would likely look into whether the Marines violated laws of war, which include prohibitions against photographing bodies and detainees and a range of other rules.
Mujahid urged the U.N. and other international groups to end such actions by U.S. troops.
On Wednesday, the Council on Islamic-American Relations, a prominent Muslim civil rights and advocacy group based in Washington, protested the video in a letter to Panetta.
"We condemn this apparent desecration of the dead as a violation of our nation's military regulations and of international laws of war prohibiting such disgusting and immoral actions," the group wrote.
"If verified as authentic, the video shows behavior that is totally unbecoming of American military personnel and that could ultimately endanger other soldiers and civilians," the letter said.