Afghan President Hamid Karzai today condemned as “ completely inhumane” a video that purports to depict four U.S. Marines urinating on the corpses of Taliban fighters. Pentagon officials said commanders believe they have identified the men’s unit and that it is back in the United States.

The Marine Corps said Wednesday it was investigating the YouTube video but had not yet verified its origin or authenticity. The case has been referred to the Naval Criminal Investigative Service, the Navy’s worldwide law enforcement organization.

In a statement, Karzai called on the U.S. military to punish the Marines. The Afghan Ministry of Defense also condemned the actions in the video, which it described as “shocking.”

The NATO- led security force in Afghanistan released a statement today saying, “ This disrespectful act is inexplicable and not in keeping with the high moral standards we expect of coalition forces.”

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.

Sen. John McCain, a Navy veteran who fought and was held prisoner in the Vietnam war, said the incident “makes me so sad.”

McCain, the top Republican on the Senate Armed Services Committee, called the Marine Corps one of America’s strongest institutions and said its image has apparently been tarnished by “a handful of obviously undisciplined people.”

“There should be an investigation and these young people should be punished,” McCain, R-Ariz., said today on “CBS This Morning.”

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.