Defense Secretary Donald Rumsfeld has denounced as deeply disturbing and un-American the abuse of Iraqi prisoners by U.S. military personnel. Mr. Rumsfeld is promising those responsible will be held accountable.

Mr. Rumsfeld says he is personally stunned by the cases of abuse, including instances in which Iraqi prisoners were sexually humiliated by U.S. soldiers.

Speaking to reporters at the Pentagon, the grim-faced Defense Secretary calls the actions unacceptable but insists they are an exception. "The images that we've seen that include U.S. forces are deeply disturbing, both because of the fundamental unacceptability of what they depicted and because the actions by U.S. military personnel in those photos do not in any way represent the values of our country or the armed forces," he said.

Mr. Rumsfeld says those responsible will be punished. "We're taking and will continue to take whatever steps are necessary to hold accountable those who may have violated the code of military conduct and betrayed the trust placed in them by the American people," he said.

Six military personnel are already facing criminal prosecution in connection with the incidents, first uncovered by the military in January. At least six other military personnel have been reprimanded and two removed from their duties. Investigations are continuing.

Mr. Rumsfeld declines to say whether he believes the abuse cases have damaged U.S. attempts to establish trust in Iraq.

But he says he believes any damage that has been done to the U.S. image will diminish over time. "The world has seen problems of this type before, and I regret to say I'm afraid that people do things that they ought not to do, and that are harmful, and that are disappointing and are, in many instances, disgraceful," he said.

The abuse cases have stirred widespread anger, from the Middle East to the U.S. Congress. Human Rights groups have called for special investigations.

The Army has meanwhile announced investigations have been launched into 35 incidents of alleged prisoner abuse in both Afghanistan and Iraq since December 2002. Officials say 25 of the cases involve deaths in custody, including two alleged homicides of inmates by soldiers and one instance in which a prisoner was killed while trying to escape.

In another development, Defense Secretary Rumsfeld says the Pentagon has decided to keep the U.S. troop level in Iraq at around 135,000 soldiers for longer than planned.

Twenty-thousand troops already in Iraq were recently notified they would be staying in the country three months longer than scheduled to maintain that level. Now Mr. Rumsfeld says additional forces are being identified to replace those soldiers after their 90-day extension tours are over.