An invitation to visit the Guantanamo prison camp issued by US authorities has been formally rejected by the UN because of restrictions imposed by Washington denying UN officials the right to speak to detainees in private.

UN human rights experts say private interviews with detainees would be necessary to give "credible, objective and fair assessment of the situation of the detainees".

So far only the Red Cross has been given access to the 500 terror suspects currently being held at the US military camp.