U.S. military officials have blocked a top U.N. official from privately seeing accused whistleblower, U.S. Army Private Bradley Manning, who has been held in solitary confinement at a military prison since July. Juan Méndez, the U.N. special rapporteur on torture, said he was “deeply disappointed and frustrated” that he was not allowed to have an unmonitored visit with Manning. Méndez has been seeking to determine whether Manning’s confinement at a military brig amounts to torture. Manning is accused of leaking thousands of classified U.S. military and diplomatic documents to WikiLeaks. On Sunday, the New York Review of Books published a letter signed by more than 250 lawyers, professors and authors that called the conditions of Manning’s confinement “illegal and immoral.” The list of signatories includes Laurence Tribe, a Harvard professor who taught constitutional law to Barack Obama. Tribe was a key backer of his 2008 presidential campaign.