Two British men who were released from the Guantanamo Bay prison and repatriated in March charged in a letter sent yesterday to President Bush that they had been physically abused during their two years in detention there.

Shafiq Rasul, 26, and Asif Iqbal, 22, said U.S. military officials' statements that no Guantanamo Bay detainees were stripped naked, physically abused or humiliated were "completely untrue."

"From the moment of our arrival in Guantanamo Bay and indeed from long before, we were deliberately humiliated and degraded by the use of methods that we now read U.S. officials denying," the pair said in the letter, which was also sent to members of the Senate Armed Services Committee.

Yesterday evening, U.S. military officials strenuously stood by those assertions. "Their allegations are simply false," said Army Col. David McWilliams, a spokesman for the U.S. Southern Command, the military unit that oversees the jail for alleged al Qaeda and Taliban fighters in Cuba where about 600 detainees are held. "Those things they allege didn't happen in Guantanamo." He noted that he had not read their letter to the president and was responding to descriptions of their claims related by a reporter.

Also yesterday, the International Committee of the Red Cross, which is granted unrestricted access to detainees at the U.S. military facility, said it had sent a report to U.S. government officials early this month that summarized its findings after a visit to the island jail in February and March. But Red Cross officials, citing their policy, declined to describe the report's contents.

The former detainees' allegations follow U.S. acknowledgment that some troops guarding Iraqi prisoners in Baghdad's Abu Ghraib prison physically abused and humiliated them. While many human rights groups have asserted that prisoners have been held far too long in Guantanamo Bay without due process, the government has acknowledged only a handful of excessive-force cases there.

Rasul and Iqbal wrote that during interrogations, they were chained to the floor for so long that at times they urinated in their chairs. They added that one innovation launched by Maj. Gen. Geoffrey D. Miller, the former Guantanamo Bay commander who recently helped redesign interrogation techniques in Iraq, was what interrogators called "short-shackling." This technique forced detainees to squat without a chair with hands chained between their legs to the floor, they wrote.

"If we fell over, the chains would cut into our hands," their letter said. The interrogations sometimes lasted many hours, and the air conditioning sometimes made the room uncomfortably cold, they added. "There was strobe lighting and loud music played that was itself a form of torture," they wrote. "Sometimes dogs were brought in to frighten us."

McWilliams said, however, that "our protocols at Guantanamo absolutely forbid us to strip detainees naked for interrogations, to physically abuse them or to subject them to extremes of hot or cold. . . . The kinds of things that would humiliate a detainee or cause harm, we don't use."

On Sunday, The Washington Post quoted defense officials saying that in April 2003, the Pentagon approved interrogation techniques for use at Guantanamo Bay that allowed the reversal of some detainees' normal sleep patterns, as well as exposing them to heat, cold and "sensory assault," including loud music and bright lights.

The classified list of about 20 techniques was approved at the highest levels of the Defense and Justice departments, and was the first publicly known evidence of an official policy that allowed interrogators to use physically or psychologically stressful tactics.

Rasul and Iqbal made similar claims of abuse to reporters when they were released and sent home two months ago. Among their other assertions were that they were tricked into falsely confessing that they had met al Qaeda mastermind Osama bin Laden and Mohamed Atta, who planned the Sept. 11, 2001, attacks.