President George Bush has said he is "sorry for the humiliation suffered by the Iraqi prisoners" in US custody.
His comments came a day after he was criticised for failing to apologise during interviews with two Arab TV channels on the abuse scandal.
The photo furore grew on Thursday with the release of more shocking pictures.
Mr Bush confirmed Defence Secretary Donald Rumsfeld would stay in the cabinet, but said Mr Rumsfeld should have told him earlier about the abuse.
Such a public rebuke is an unprecedented acknowledgement of presidential displeasure, says the BBC's Justin Webb in Washington.
He says Mr Rumsfeld could be in still deeper trouble if he fails to offer words of contrition - however much that goes against his natural instincts - when he appears before the Senate Armed Services Committee on Friday.
'Sick to my stomach'
Mr Bush was speaking in the White House's Rose Garden after talks with Jordan's King Abdullah.
He told reporters that he had told King Abdullah he was "sorry for the humiliation suffered by the prisoners and the humiliation suffered by their families".
Mr Bush said sorry twice during his statement - the first time he has apologised for what happened.
Challenged on the position of Mr Rumsfeld, Mr Bush said: "I told him I should have known about the pictures and the report" on the affair by the Pentagon, completed two months ago.
Mr Bush has said he only realised the extent of the abuse when he saw the pictures on television.
But he insisted that he still supported Mr Rumsfeld, who he said "has served our nation well. He is an important part of my cabinet and he'll stay in my cabinet".
The Bush administration has faced widespread revulsion over the photographs of laughing US troops next to Iraqi prisoners in humiliating, often sexual, poses.
Mr Bush said they had made Americans "sick to our stomachs" - and repeated his insistence the photos did not reflect "the true nature and heart of America".
Calls to quit
There have been more calls for Mr Rumsfeld's resignation from senior Democrat figures.
On the campaign trail in California, presumptive Democratic presidential nominee John Kerry said he had called on Mr Rumsfeld to quit "months ago" because of miscalculations on Iraq.
Mr Kerry said the abuse scandal only
"compounds" the evidence for him to step down.
"I think he should have and I think he should have now," Mr Kerry said, according to Reuters news agency.
Nancy Pelosi, the most senior Democrat in the House of Representatives, said Mr Rumsfeld had been engaged in a "cover-up" of the allegations of abuse and should resign.
Tom Harkin also called for him to go, the first member of the US Senate to do so.
There has been widespread criticism from US politicians that once the Pentagon knew the scale of the abuse - and in particular that it was depicted in graphic photos which would be broadcast - it should have done more to inform Congressional committees.
The scandal, which Mr Bush acknowledges has had a "terrible" impact on the US' standing across the Middle East, was fuelled again on Thursday with the publication of more photos.
As well as the photo of the soldier with a prisoner on a dog leash, another picture released in the US press shows a soldier giving a thumbs-up sign next to what appears to be a corpse.
The Washington Post says it cannot eliminate the possibility that some of the latest images were staged, but reporter Christian Davenport says he believes the pictures are authentic.
He said they were taken in mid-2003 and were scattered among about 1,000 images that also include photos of soldiers posing on camels and general life in the American military in Iraq.
Meanwhile, the International Committee of the Red Cross has said that it repeatedly urged the US to take "corrective action" at Abu Ghraib.
The ICRC, which visits prisoners held by coalition authorities in Iraq, had previously refused to comment publicly on conditions at the prison.