US Defence Secretary Leon Panetta. - File Photo.

WASHINGTON: Defense Secretary Leon Panetta on Thursday condemned as ''utterly deplorable'' a video that purports to depict four US Marines urinating on the corpses of Taliban fighters. He said such behavior is ''entirely inappropriate for members of the United States military'' and those responsible will be held accountable.

Panetta said he had ordered the Marine Corps and Marine Gen. John Allen, the top commander of the Nato-led forces in Afghanistan, to fully investigate.

The Marine Corps said Wednesday it would investigate 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 arm.

The video, posted on the Internet, shows men in Marine combat gear, standing in a semi-circle over three bodies. It is not clear whether the dead were Taliban or civilians or someone else. The title on the posting called them Taliban insurgents but it was unclear who added that title, Marine Corps officials in Washington said.

The reaction from Afghanistan was angry. Afghan President Hamid Karzai condemned the video as ''completely inhumane.''

The Afghan Defense Ministry called it ''shocking.'' And the Taliban issued a statement accusing US forces of committing numerous ''indignities'' against the Afghan people.

''First they killed the Afghans with mortars, and they then urinated on their bodies,'' Taliban spokesman Zabiullah Mujahid said. ''We strongly condemn this inhumane action by the wild American soldiers.''

Panetta said the actions, if true, were inexcusable.

''I have seen the footage, and I find the behavior depicted in it utterly deplorable. I condemn it in the strongest possible terms,'' Panetta's statement said. ''Those found to have engaged in such conduct will be held accountable to the fullest extent.''

The video came to light at a delicate time in relations among the United States, Afghanistan's elected government and the Taliban insurgency fighting for both territorial control and cultural and religious preeminence in Afghanistan.

The US is trying to foster peace talks between the Karzai government and the Pakistan-based Taliban high command, and has made unprecedented offers to build trust with the insurgents, including the planned opening of a Taliban political office to oversee talks.