The U.S. Marine Corps said Wednesday it's investigating a 39-second online video in which four men dressed in Marine uniforms appear to urinate on three lifeless bodies.
It's unclear if the bloodied bodies are Taliban fighters.
Some of the men can be heard chuckling, while another says: "Have a great day, buddy," apparently to one of the corpses.
"You got it on video?" one of the men asks, glancing toward the camera.
The Marine Corps said it has not verified the origin or authenticity of the video. It's not clear who shot it or how it surfaced on websites like LiveLeak and YouTube.
In a statement, the Marine Corps said the actions portrayed in the video are "not consistent" with Marine values.
Citing an anonymous defence official, the Associated Press reports the case will be referred to the Naval Criminal Investigative Service, the U.S. Navy's worldwide law enforcement organization.
The video could spark retaliation against American troops in Afghanistan and outrage across the Muslim world.
The Council on Islamic-American Relations, a prominent Muslim civil rights and advocacy group based in Washington, has condemned the video.
"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 in a letter faxed to Defence Secretary Leon Panetta, the Associated Press reports.
"If verified as authentic, the video shows behaviour that is totally unbecoming of American military personnel and that could ultimately endanger other soldiers and civilians," the letter said.
A Pentagon spokesman, Navy Capt. John Kirby, told the AP the video is deeply troubling.
"Whoever it is, and whatever the circumstances, which we know is under investigation, it is egregious behaviour," Kirby said.
There are some 20,000 Marines among the 90,000 U.S. troops still stationed in Afghanistan. The U.S. government has set a 2014 deadline for the withdrawal of all troops from the country.
