Afghan president Hamid Karzai has strongly condemned a video posted on the internet which appears to show US soldiers in Afghanistan urinating on corpses.
It was unclear whether the dead bodies were those of civilians or Taliban fighters.
"The government of Afghanistan is deeply disturbed by a video that shows American soldiers desecrating dead bodies of three Afghans," said a statement from Karzai's office on Thursday.
"This act by American soldiers is simply inhuman and condemnable in the strongest possible terms."
The footage, first posted on the Live Leak website, shows four men in military uniforms urinating on three bloodied bodies on the ground, apparently aware that they were being filmed.
In a phone call to Karzai, Leon Panetta, the US defence secretary, expressed his regret over the incident and promised an investigattion.
"I have seen the footage, and I find the behaviour depicted in it utterly deplorable. I condemn it in the strongest possible terms," Panetta said in a statement.
Panetta has ordered the Marine Corps and General John Allen, the US commander of international forces in Afghanistan, to immediately and fully investigate the incident.
"This conduct is entirely inappropriate for members of the United States military ... Those found to have engaged in such conduct will be held accountable to the fullest extent," he said.
Hillary Clinton, the US Secretary of State, has also expressed "dismay" and condemned the "deplorable behavior".
The international coalition forces in Afghanistan, as well as the US embassy in Kabul, have also strongly condemend the video.
About 20,000 marines are deployed in Afghanistan, mostly in Kandahar and Helmand provinces, in the south of the war-ravaged country.
Al Jazeera’s Rosiland Jordan, reporting from Washington, said the video will make the work of US forces in the country much more difficult.
"The timing could not be more difficult. The US is trying to work out efforts to engage in direct peace talks with the Taliban, it is trying to support the Afghan government’s efforts to promote reconciliation," she said.
In a statement, the Taliban said the incident was "against all international human rights" but "not the only example of the horrific actions that the Americans have done in Afghanistan".
"American soldiers are trained to spread horror and this is one of the examples," the Taliban said.
However, the group's statement added that the incident would not affect negotiations with the US after US officials said Washington would send an envoy to Afghanistan to prepare the ground for direct peace talks between the two sides.
Lieutenant Colonel Jay Stout, a former US Marine Corps pilot, told Al Jazeera he found the incident "disturbing".
"Look, marines kill to win, and sometimes they kill a lot and that's good, that's fine, that's war," he said.
"But in victory we are trained to be compassionate, we are trained to be respectful and this incident was neither of those."
The US military has been prosecuting soldiers from its army's Fifth Stryker Brigade on charges of murdering unarmed Afghan civilians while deployed in 2010 in Kandahar province.
In that case, photographs published last March by two magazines - Der Spiegel and Rolling Stone - showed soldiers posing with the bloodied corpse of an Afghan boy they had just killed.