US troops are seen posing with the maimed bodies of suspected Afghan insurgents in photos published on Wednesday, an incident that threatened to further fray US-Afghan ties and prompted yet another apology from Washington for soldiers' misbehaviour.
In one of the pictures, a US paratrooper posed next to an unofficial patch placed beside a body that read "Zombie Hunter," while in another photo soldiers posed with Afghan police holding the severed legs of an insurgent bomber.
Two soldiers in another photo held a dead insurgent's hand with the middle finger raised.
US officials quickly condemned the behaviour seen in the pictures published by the Los Angeles Times.
While it was too soon to say whether the photos - which date from 2010 - would cause a violent backlash in Afghanistan, they extend a series of events that have embarrassed the White House and complicated President Barack Obama's South Asia strategy.
In recent months, a video circulated of Marines urinating on corpses that were apparently those of Afghan insurgents; US troops burned copies of the Koran, the Muslim holy book, prompting riots; and a US soldier left his base in a rural province and allegedly slaughtered 17 Afghan civilians.
In neighbouring Pakistan, relations sunk to a new low after a disputed November incident in which a US airstrike killed 24 Pakistani soldiers. Washington has not apologised in that case.
During a meeting of NATO allies in Brussels on Wednesday, Defense Secretary Leon Panetta apologised for the latest incident "on behalf of the Department of Defense and the US government" and said "that behaviour is unacceptable."
White House spokesman Jay Carney told reporters aboard Air Force One as Obama flew to Ohio for an economic speech, "The conduct depicted in those photos is reprehensible."
Carney said Obama was briefed on the matter but he did not know whether the president had seen the photos, which the Los Angeles Times said it received from a soldier.
The incident dealt another blow to already tense US and NATO ties with Afghanistan.
"That behaviour that was depicted in those photos absolutely violates both our regulations and more importantly our core values," Panetta told a news conference, adding that the pictures were under investigation.
"I know that war is ugly and it's violent and I know that young people sometimes caught up in the moment make some very foolish decisions," he added. "I'm not excusing that behaviour, but neither do I want these images to bring further injury to our people and to our relationship with the Afghan people."
The photos could stir up more anti-Western sentiment in Afghanistan as NATO combat troops look to exit the country in 2014 and strengthen fragile security.
Such incidents have complicated US efforts to negotiate a strategic partnership agreement to define its presence once most foreign combat troops pull out by the end of 2014.
Panetta said he regretted the Times' decision to publish some of the photos, which he said might trigger retaliatory violence against foreign soldiers stationed in Afghanistan.
Pentagon Press Secretary George Little said US forces in Afghanistan were taking security measures to protect against a possible backlash over the photographs, adding that the images could be "used by the enemy to incite violence."
The Times said the photographs were of suicide bombers and insurgents. Reuters was unable to independently confirm whether they were insurgents or ordinary Afghans caught up in violence.
The US Army said it launched an investigation into the 18 photographs taken by members of the 82nd Airborne Division as soon as The Times showed them to military authorities, who had appealed for the newspaper not to publish them.
The Times said it obtained the pictures from a member of the unit who demanded anonymity and was concerned the photographs were evidence of a breakdown in leadership and discipline that threatened the security of the troops.
"The actions of the individuals photographed do not represent the policies of International Security Assistance Force or the US Army," the commander of international forces in Afghanistan, US General John Allen, said in a statement.
The burning of copies of the Koran at a major NATO airbase triggered a week of riots that left 30 dead and led to the deaths of six Americans.
The March rampage by a US Army sergeant in two southern Afghan villages, in which 17 civilians were killed, prompted Afghan President Hamid Karzai to demand foreign soldiers confine themselves to major bases.
Taliban insurgents launched suicide attacks in Kabul and three other provinces during the weekend, claiming the assault was launched in retaliation for all of the incidents.
The Times said the photographs were taken at a difficult time for the 82nd Airborne in Afghanistan, and virtually all of the soldiers in the pictures had friends who were killed by homemade bombs or suicide bombers.
The soldiers initially were sent to collect evidence to help identify the body of a suicide bomber at a police station in Afghanistan's Zabol province in February 2010.
They revisited several months later to collect evidence to help identify three suspected insurgents killed when they accidentally detonated a bomb they were building. The soldiers took pictures with remains on both visits, The Times said.
Within that time frame, the commander and top noncommissioned officer of one battalion were relieved of duty and ordered home after slides with racial and sexist overtones were shown during daily briefings, the Times said.
And turmoil at the unit's home base in North Carolina prompted the commander to bar the wife of a senior commander in Afghanistan from interacting with her husband's brigade, saying her influence was "detrimental to the morale and well-being of the unit," The Fayetteville Observer reported.
The Times defended its publication of the photos.
"After careful consideration, we decided that publishing a small but representative selection of the photos would fulfil our obligation to readers to report vigorously and impartially on all aspects of the American mission in Afghanistan," Times Editor Davan Maharaj said in the newspaper's article.
But Navy Captain John Kirby, a Pentagon spokesman, noted that the photographs were two years old and bore no relevance to current security or leadership issues. "The only thing that made the story 'news' is the graphic nature of the imagery," he said. "Take that away, and you've got little of substance."