All four US Marines seen in an online video apparently urinating on corpses in Afghanistan have been identified, and two of them have been questioned, US military officials have said.
An official said on Friday that two men "have been questioned" by the Naval Criminal Investigative Service over the disturbing footage but are "not in custody".
The official, who asked not to be named because of the ongoing probe, confirmed the Marines seen in the graphic footage are from a sniper unit in the 3rd Battalion, 2nd Marines based at Camp Lejeune in North Carolina, and that the two men questioned are both on active duty.
Tracking down the other two Marines took longer, apparently because they had been transferred from Camp Lejeune, said the official. But the US military confirmed all four men have now been identified.
That unit served in Afghanistan's Helmand province from March until September of 2011, the official said. The remaining two soldiers have since moved on to other units.
The footage, which appeared on the internet, appears to show four men in military uniforms urinating on three bloodied bodies on the ground, apparently aware that they were being filmed.
Leon Panetta, the US defence secretary, accepted the video as genuine, saying in a statement: "Those found to have engaged in such conduct will be held accountable to the fullest extent."
In a phone call to Afghan President Hamid Karzai, Panetta expressed his regret over the incident and promised an investigation.
"I have seen the footage, and I find the behaviour depicted in it utterly deplorable. I condemn it in the strongest possible terms," Panetta's statement said. "This conduct is entirely inappropriate for members of the United States military."
He ordered the Marine Corps and General John Allen, the US commander of international forces in Afghanistan, to immediately and fully investigate the incident.
Hillary Clinton, the US Secretary of State, also expressed "dismay" and condemned the "deplorable behavior".
"By acknowledging this video's existence almost from the moment that they learned of it, the US Marine Corps, the US military, indeed the entire US government is trying to tamp down international reaction that would have a negative impact on the US mission in Afghanistan," said Al Jazeera's Rosiland Jordan, reporting from Washington.
"This is a situation that does worry officials here in Washington because they know that no matter how quickly they condemn these sorts of actions, even though they say they are rare, they also know that the reaction from people who will see this is really uncontrollable.
"They can't tell people that the Americans can be trusted when things like this circulate on the internet," Jordan added.
Our correspondent said the video would make the work of US forces in the country much harder.
"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 Afghanistan, the video was condemned by Karzai, the ISAF international coalition and by the Taliban.
"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.
"This act by American soldiers is simply inhuman and condemnable in the strongest possible terms."
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.
"We also call on the United Nations and other Human Right groups to block such inhumane acts of the hypocritical America and put into practice the humanitarian slogans which are always exclaimed by these organisations," the group added.
However, the statement also said 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.
"This is not a political process, so the video will not harm our talks and prisoner exchange because they are at the
preliminary stage," said spokesman Zabihullah Mujahid.
About 20,000 marines are deployed in Afghanistan, mostly in Kandahar and Helmand provinces, in the south of the war-ravaged country.
Over the years of combat in Iraq and Afghanistan, officials periodically have been stunned by the troops' penchant for taking photos or videos of themselves engaged in inappropriate or criminal acts.
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.