A group of 31 U.N. human rights investigators issued a rare joint appeal to the United States to give them access to detention centers in Iraq, Afghanistan and Guantanamo Bay, Cuba.

The request came at the end of a week-long meeting in Geneva on the impact of the U.S.-led counterterrorism campaign on human rights. It signaled mounting frustration over the Bush administration's refusal to open the doors of its detention centers to U.N. human rights monitors.

The statement asks that four specialists -- trained to check for evidence of torture, arbitrary detention, medical and physical abuse, and judicial independence -- be invited to Iraq, Afghanistan and Guantanamo Bay "at the earliest possible date" to determine whether the human rights of prisoners are "properly upheld." They would present their findings to the U.N. Commission on Human Rights.

"The way prisoners are treated in Iraq, Afghanistan and Guantanamo is totally contrary to international law and humanitarian law," said Doudou Diene of Senegal, the United Nations' special rapporteur for racism and discrimination. We want to "send a team of special rapporteurs to go and visit those places."

U.S. officials said that they are providing detainee access to representatives of the International Committee of the Red Cross and they see no need for the United Nations' rights experts to duplicate that work.

Richard Grenell, the spokesman for the U.S. mission to the United Nations, said the Bush administration was "very disappointed" that the United Nations' human rights investigators had singled out the United States for criticism when they "have plenty to do" investigating abuses in places such as Zimbabwe, North Korea and Cuba.

"The International Committee of the Red Cross has full access," Grenell said. "I don't think the U.N. human rights rapporteurs should be placing this as a priority knowing there are other human rights priorities around the world."

Although the United States grants the Red Cross access to its main detention facilities in Iraq, Afghanistan and Guantanamo Bay, it has sought to prevent the organization from interviewing some of the most important detainees.

In addition, ICRC spokeswoman Amanda Williamson said, the organization has been pressing the Bush administration to provide "access to people held in undisclosed places of detention."

"We haven't been granted access yet, but the dialogue still continues," she said.

The treatment of prisoners of war is governed by the Geneva Conventions, which requires combatants to provide access to the International Committee for the Red Cross.

U.S. officials say that they have no obligation to grant access to human rights investigators. "Their position is that it's a question of international humanitarian law and the Geneva Convention and not a human rights issue," said a U.N. official.

The Bush administration has rebuffed previous requests by the acting U.N. high commissioner for human rights, Bertrand Ramcharan, and by other U.N. human rights units to visit Guantanamo.

But Ramcharan published eyewitness accounts by several detainees who alleged they were subjected to arbitrary arrest and beaten while in detention in Iraq.

Saddam Salah Abood Rawi, 29, interviewed by U.N. officials in Amman, said in the June 9 report that American guards at the Abu Ghraib prison in Iraq had kicked and beaten him, knocking out two teeth.

Grenell criticized the report, saying that the United States was "disappointed that some of the reports findings allege human rights violations in very general terms and fail to indicate where and when such abuses occurred."