The White House and the Pentagon have voiced regrets over newly published photographs that claim to show US troops posing with the bodies of dead insurgents in Afghanistan.
Defence secretary Leon Panetta called them a violation of America's "core values".
"My apology is on behalf of the department of defence and the US government," Mr Panetta told a news conference after a Nato meeting in Brussels.
At the White House, President Barack Obama's chief spokesman, Jay Carney, echoed Mr Panetta's comments, saying the incident was "reprehensible".
It is the latest in a series of recent Afghan battlefield embarrassments for the United States, and comes at a time when Washington is still working with President Hamid Karzai in Kabul to smooth over strained relations.
Mr Carney said the picture-taking incident does not represent the standards of the US military and said that Mr Obama believes the situation needs to be investigated and those responsible held accountable. He said he did not know if the president had seen the photographs.
The photos were published in the Los Angeles Times. One shows members of the 82nd Airborne Division posing in 2010 with Afghan police and the severed legs of a suicide bomber.
The same platoon a few months later was sent to investigate the remains of three insurgents reported to have accidentally blown themselves up - and soldiers again posed for photographs with the remains, the newspaper said.
A photo from that incident appears to show the hand of a dead insurgent resting on a US soldier's shoulder as the soldier smiles. Top US military and civilian officials rushed to condemn the soldiers' actions, calling them repugnant and a dishonour to others who have served in the conflict. The Army said an investigation is under way.
Mr Panetta said he condemned the behaviour, but said: "This is war. I know that war is ugly and it's violent, and I know that young people sometimes caught up in the moment sometimes make very foolish decisions."