US Senator Dick Durbin on Wednesday refused to apologise for comments he made on the Senate floor referring to Nazis, Soviet gulags and a "mad regime" like Pol Pot's Khmer Rouge in Cambodia.
Illinois Republican party chairman Andy McKenna had demanded he apologise.
"Senator Durbin's comments come as a great disservice to our military personnel in Guantanamo," he said.
"They are also a great disservice to all US soldiers and veterans who have fought, and continue to fight, to overcome evil regimes and spread democracy around the world."
Durbin did not plan to apologise for the comments, spokesman Joe Shoemaker said.
"This administration should apologise to the American people for abandoning the Geneva Conventions and authorising torture techniques that put our troops at risk and make Americans less secure," Durbin had said in a statement on Wednesday evening.
During a speech on Tuesday, Durbin, the Senate's number two Democrat, quoted from an FBI agent's report describing detainees at the naval base in Cuba as being chained to the floor without food or water in extreme temperatures.
"If I read this to you and did not tell you that it was an FBI agent describing what Americans had done to prisoners in their control, you would most certainly believe this must have been done by Nazis, Soviets in their gulags, or some mad regime - Pol Pot or others - that had no concern for human beings."
"You would most certainly believe this must have been done by Nazis, Soviets in their gulags, or some mad regime - Pol Pot or others - that had no concern for human beings"
US Senator Dick Durbin
Durbin is not alone in his criticism.
Human-rights groups have long accused the administration of unjustly detaining suspects at the prison camp. Amnesty International last month called the detention centre the "gulag of our times".
President George Bush and other administration officials, however, have strongly resisted such comparisons and questioned Amnesty's objectivity.
"It's difficult to explain to a mom and dad who's lost their son or daughter how you can have someone in Guantanamo Bay, release them and then they kill your son and daughter"
"I take strong exception to any characterisations that try to
diminish what our military is doing and the standards and values that they adhere to," White House spokesman Scott McClellan said.
The Bush administration calls the Guantanamo prisoners enemy combatants who are entitled to fewer legal protections than those afforded to prisoners of war under the Geneva Conventions.
According to US Attorney-General Alberto Gonzales on Wednesday, the US government often considers whether it would be better to stop detaining prisoners at Guantanamo.
Gonzales (L) has defended the
right to hold enemy combatants
"That's a question that is evaluated, I would say, quite often," he said in Sheffield, England, where he will attend a meeting of G8 interior ministers on Thursday and Friday.
On Wednesday, he had said "there will of course be an end", but did not specify when.
He also pointed out that about a dozen of those who had been released had returned to fight against the US.
"It's difficult to explain to a mom and dad who's lost their son or daughter how you can have someone in Guantanamo Bay, release them and then they kill your son and daughter," he said.
Since the camp was set up after the 11 September 2001 attacks on the US, 167 detainees have been freed and 67 others released to the custody of their home governments.
About 520 detainees from about 40 countries remain at Guantanamo. Only 12 have been handed over to military commissions for investigation of possible war crimes and four have been charged.
In a three-hour hearing of the Senate Judiciary Committee on Wednesday, legal experts from the US military and the Justice Department said the US had a right under the Geneva Conventions to hold enemy combatants.
But committee chairman Senator Arlen Specter suggested lawmakers would have to clarify what he called a "crazy quilt" of laws and regulations governing the detentions.
Some lawmakers want the facility closed, saying it has become a liability that inflames Muslims against the United States.
"Guantanamo is an international embarrassment to our nation, to our ideals and it remains a festering threat to our security," Senator Patrick Leahy, the top Democrat on the Judiciary Committee, said.
A Pew Research Centre poll, taken over the weekend, indicated most Americans agree that reports of abuse at Guantanamo are isolated incidents, and 39% think the news media is paying too much attention to the issue.
The poll found a sharp partisan divide on the issue - Democrats believing the abuses to be systemic and Republicans saying they were isolated incidents.