The U.S. government has invited three U.N. human rights experts to visit the detention center at Guantanamo Bay, Cuba, amid growing concerns of rights violations and claims that the health of some hunger-striking detainees is deteriorating.

It is unclear whether the three U.N. special rapporteurs will accept the invitation -- which was extended yesterday after nearly four years of U.N. requests to inspect the facility -- because the Defense Department plans to impose fairly strict guidelines on any visit. Guantanamo Bay holds more than 500 detainees, and current guidelines would not allow the U.N. experts direct access to prisoners.

"The department has determined on an exceptional basis to extend this invitation," according to a Pentagon news release yesterday. "The department strives for transparency in our operation to the extent possible in light of security and operational requirements and the need to ensure the safety of our forces."

The Defense Department so far has allowed only the International Committee of the Red Cross to fully examine the facility, but the results of its regular visits are kept confidential under the ICRC policy of not reporting abuses or its concerns publicly. Foreign delegations have visited some detainees who are nationals of their countries, according to defense officials, and some detainees have lawyers who have visited on a limited basis.

Calls to two U.N. officials yesterday were not returned.

Defense officials said yesterday that the U.N. visit would allow the experts to "observe operations" at the facility and to "ask questions of the command, staff and U.S. officials who would accompany them."

Such a visit could be similar to the tour that members of Congress and the media have taken in recent months. It includes very limited viewing of the lowest-security prisoners from a distance, examining empty cells and vacant cellblocks, and perhaps observing an interrogation. Visitors are not provided direct contact with detainees.

The invitation could afford the Defense Department an opportunity to tell the world, through independent international observers, that it has cleaned up its act at Guantanamo Bay, where serious abuses were alleged to have occurred and where detainees regularly report mistreatment to their attorneys. But such U.N. experts usually demand private access to detainees to determine whether mistreatment is taking place.

Tom Malinowski, Washington advocacy director for Human Rights Watch, said yesterday that it is unlikely the U.N. rapporteurs would be satisfied with a cursory look at Guantanamo Bay.

"Even in places like China, the rapporteurs on torture and arbitrary detention have been able to speak privately to prisoners in the facilities they've been allowed to visit," Malinowski said, "and even then they haven't been fully satisfied with the access they've gotten."

A guard keeps watch at the detention facility at Guantanamo Bay, Cuba, which has been the subject of accusations of human rights violations.