The Human Rights Watch organization says the United States has operated at least one secret prison in Afghanistan, where detainees were subjected to torture and other mistreatment.

Human Rights Watch terrorism researcher John Sifton says eight detainees who are now at Guantanamo have given similar, but independent, accounts of being held for up to six weeks in Afghanistan, in what they refer to only as a "dark prison."

"What we're concerned about is besides the military detention facilities in Afghanistan, which we already knew existed, what we have here is proof of a CIA prison, a secret prison, where the Red Cross has no access. And on top of that, detainees who have gotten out have allegations of mistreatment and possibly even torture," he said.

A CIA spokesman contacted to confirm or deny the allegations said his agency had no comment. The Pentagon says there are no secret prisons, and adds that there is no torture allowed at U.S. military facilities.

Human Rights Watch says the secret facility is one of several it believes existed at various times, between 2002 to 2004. The group did not speak directly to the detainees, but obtained accounts in which the suspects described to their lawyers how they were chained to walls, deprived of food and water, and kept in total darkness with blaring loud music.

Mr. Sifton accused the CIA of running the secret facilities, saying he believes they are housing what his organization calls "ghost detainees," or suspects who have just disappeared. "There are at least 26 ghost detainees that we know of, and possibly more, who are held outside of military custody, in CIA custody. So, there's no doubt that there are secret prison facilities somewhere in the world. It's just a question of where those facilities are at any given point in time. What this statement today shows, for some time, one of the secret facilities was in Afghanistan. But there are other facilities that were in other places at other times," he said.

Mr. Sifton says these other places include Eastern Europe, which also is the reported location of secret CIA-run prisons. The Human Rights Watch researcher says he feels it is important to have everything out in the open because of the danger of mistakes being made. He adds that it is harder to successfully prosecute a suspect using information gathered from secret detentions.

"The reason it's so despicable that the (Bush) Administration has held actual suspected terrorists, not because we (human rights activists) care or have sympathy for suspected terrorists, if that's what they are, but because if they are criminals who are guilty of terrorism, the administration has made it extremely difficult now to prosecute them, because all the evidence gathered from their harsh interrogations, from their illegal detention, is going to be inadmissible in any court trial. And so, it will be very difficult to ever hold them accountable for the crimes they've committed," he said.

He said his group is calling for an independent investigation into the allegations of mistreatment and secret detention. He also urged Congress to pressure the Bush Administration for an explanation.