WASHINGTON (Reuters) -- A human rights group said Sunday that the United States operated a secret prison for terrorism suspects as recently as last year in Afghanistan, where detainees where subjected to torture and other mistreatment.

The Bush administration has faced international criticism over detainees after a November 2 Washington Post article said the CIA held dozens of terrorism suspects in secret prisons called "black sites" in countries around the world, including eastern Europe.

Human Rights Watch said eight detainees now held in the U.S. military facility at Guantanamo Bay, Cuba, have told their attorneys that they were arrested separately in countries in Asia and the Middle East and flown to Afghanistan at various times between 2002 and 2004.

The men were taken to a prison near Kabul where they were shackled to walls, kept in darkness for weeks, deprived of food and water for days at a time, bombarded with loud rap and heavy metal music, and punched and slapped during questioning by U.S. interrogators, the group said.

"The prison may have been operated by personnel from the Central Intelligence Agency," the New York-based group said in a report released Sunday.

It said the facility, which detainees called the "dark prison," may have been closed after several prisoners were transferred to a main military detention site outside Bagram in late 2004.

"Without confirming that account in any way, I would underscore that the CIA does not torture," CIA spokeswoman Michele Neff said in response to the Human Rights Watch report.

A Human Rights Watch report at the time of the Washington Post report on CIA-run secret prisons said the group believed secret prisons were operating in Poland and Romania.

President Bush bowed to political pressure this week by agreeing to back legislation banning inhumane treatment of prisoners in U.S. custody. A week earlier, Secretary of State Condoleezza Rice visited Europe with assurances that the United States had done nothing unlawful.

In its latest report, Human Rights Watch said it was not able to speak directly with detainees and based its conclusions on accounts provided through the men's lawyers.

But the group said the allegations were credible enough to warrant an official investigation.

"The detainees offer consistent accounts about the facility, saying that U.S. and Afghan guards were not in uniform and that U.S. interrogators did not wear military uniforms," the group said.

None of the eight detainees, who include a Yemeni and an Ethiopian-born man who grew up in Britain, spent more than six weeks at a time in the facility near Kabul, the group said.