A military investigation is underway after a video depicting U.S. Marines desecrating the bodies of what appear to be dead Afghans was posted online.

Pentagon officials are working to confirm the video's authenticity but say there's no reason to believe it's a fake.

The 40-second video shows four uniformed men urinating onto dead bodies and making jokes.

"Have a great day, buddy," one voice says.

The Marines believed to be in the video have been identified as members of a 1,000-man battalion that recently completed a combat tour in Afghanistan. Officials said they returned to Camp LeJuene, N.C., where they apparently started bragging about the video.

Defense Secretary Leon Panetta called the video "utterly deplorable" and promised a full investigation.

Officials fear the video will ruin the military's reputation -- and possibly negatively impact peace talks in Afghanistan.

"The danger is that this kind of video can be misused in many ways to undermine what we are trying to do in Afghanistan and the possibility of reconciliation," Panetta said at Fort Bliss, Texas.

He added that the U.S. military must, "Send a clear signal to the world that the U.S. will not tolerate this kind of behavior and that is not what the U.S. is all about."

Desecrating dead bodies is a violation of U.S. military law and the Geneva Convention.

*Originally aired on January 13, 2012.