KABUL/WASHINGTON: A video showing what appears to be American forces urinating on dead Taliban fighters prompted anger in Afghanistan and promises of a U.S. investigation Thursday, but the insurgent group said it would not harm nascent efforts to broker peace talks. The video, posted on YouTube and other websites, shows four men in camouflage Marine combat uniforms urinating on three corpses. One of them jokes: “Have a nice day, buddy.” Another makes a lewd joke.

Afghan President Hamid Karzai condemned the video, describing the men’s actions as “inhuman” and calling for an investigation, in a statement Thursday evening.

In Washington U.S. Defense Secretary Leon Panetta telephoned Karzai to denounce the actions in the video as “deplorable” and to say it would be investigated immediately, the Pentagon said.

Although the U.S. military has stopped short of confirming the video is authentic, the Pentagon Thursday came close. Pentagon spokesman Captain John Kirby said, “We don’t have any indication that it’s not authentic.”

The video is likely to stir up already strong anti-U.S. sentiment in Afghanistan after a decade of a war that has seen other cases of abuse, and that could complicate efforts to promote reconciliation as foreign troops gradually withdraw.

The administration of U.S. President Barack Obama, seeing a glimmer of hope after months of efforts to broker talks, is launching a fresh round of shuttle diplomacy this weekend.

Marc Grossman, Obama’s special representative for Afghanistan and Pakistan, will fly into the region for talks with Karzai and top officials in Turkey, Saudi Arabia and the United Arab Emirates.

His immediate goal is to seal agreement for the Taliban to open a political office in the Gulf state of Qatar.

Despite concerns when the video first emerged that it would not help his efforts to build confidence among the warring parties, a Taliban spokesman said although the images were shocking, the tape would not affect talks or a mooted prisoner release. Panetta called the actions shown in the film “utterly deplorable” and said he had ordered the Marine Corps and the commander of the NATO-led International Security Assistance Force in Afghanistan to investigate.

“Those found to have engaged in such conduct will be held accountable to the fullest extent,” he said in a statement.

A Marine officer, speaking on condition of anonymity, told Reuters that the Marines in question were believed to be from the 3rd Battallion, 2nd Marines, which is based out of Camp Lejeune, North Carolina. The battalion returned to its home base in North Carolina last fall after a tour in Afghanistan.

An official told Associated Press the Marines had identified at least two of the four Marines in the video.

News of the footage had yet to spread in Afghanistan – a country where electricity and the Internet are limited – but Afghans who were told about what the tape appears to show were horrified.