"These events occurred on my watch. As Secretary of Defence, I am accountable for them. I take full responsibility," Rumsfeld told the Senate Armed Services Committee on Friday.
But his testimony was interrupted by a group of Anti-Rumsfeld protesters who shouted slogans, calling on Rumsfeld to be sacked.
"Fire Rumsfeld" some yelled, while others called him a war criminal.
Rumsfeld took the witness chair after a week of controversy over the photographs of US captors abusing their prisoners, often forcing them to assume sexually humiliating poses. Several Democratic lawmakers have demanded his resignation.
Rumsfeld also referred to videos of the abuse, a reference to findings in a military report that there were "numerous photos and videos of actual detainee abuse taken by detention facility personnel."
Though a number of photographs have been leaked to the media, no videotapes have been made public.
Fresh disclosures surfaced as Rumsfeld went before the committee, the first of two such appearances during the day.
More cases of US abuse of Iraqis
have surfaced in recent days
In Geneva, the International Red Cross said it had warned US officials of abuse of prisoners in Iraq more than a year ago.
"We were dealing here with a broad pattern, not individual acts. There was a pattern and a system," said Pierre Kraehenbuehl, director of operations for the International Committee of the Red Cross.
Answering a question many lawmakers have posed, Kraehenbuehl said the abuse went beyond detainees held at the Abu Ghraib prison in the Baghdad area.
Despite callsfrom Senator John Kerry and other Democrats for resignation, no congressional Republican has called on Rumsfeld to step down. And the defence secretary drew a vote of confidence on Thursday from President Bush, who declared flatly "he'll stay in my Cabinet."
But congressional Republicans made plain their unhappiness that they learned of the abuse and of the shocking photos of prisoners forced into sexually humiliating poses from the news media.
"These events occurred on my watch. As secretary of defence, I am accountable for them. I take full responsibility"
secretary of defence
Senator John Warner and Senator Carl Levin both expressed their displeasure that they had not been informed earlier.
Levin noted with "deep dismay" that Rumsfeld and General Richard Myers, the chairman of the Joint Chiefs of Staff, had briefed the panel about Iraq in a classified session last week, but did not mention the scandal the government knew was about to break in the news media.
Warner said the committee needed to know "who knew what when, what they did about it, and why were members of Congress not properly and adequately informed."
Consultation with Congress "is not supposed to be an option but a longstanding and fundamental responsibility" of administration officials, Levin lectured Rumsfeld.
The committee session was televised live in the United States and in the Arab world, as well. Aljazeera aired the proceedings live with simultaneous Arabic translation.