The Pentagon has invited United Nations officials to visit the Guantanamo Bay prison camp more than three years after first receiving the request.
Three human rights monitors will be allowed to observe the facilities and question military officials, but will not have access to detainees.
The Pentagon said the invitation showed it had nothing to hide.
Human rights activists have criticised conditions at the camp in Cuba where several inmates are on hunger strike.
A Pentagon spokesman said the UN officials would not be allowed to speak to detainees because that was the role of the International Committee of the Red Cross.
About 505 prisoners remain at Guantanamo, many of them captured in Afghanistan.
