U.N. expert "frustrated" with U.S. over WikiLeaks soldier

GENEVA (Reuters) - The United Nations investigator on torture on Monday accused the U.S. administration of blocking a one-on-one meeting he was seeking with detained "WikiLeaks" soldier Bradley Manning.

Argentine lawyer Juan Mendez said he had been trying to organize a visit to check on Manning's condition since December.

Manning, 23, is being held during the investigation of charges that while serving in Iraq he leaked secret documents, including hundreds of State Department cables, that later appeared on the Wikileaks website.

Manning has been held at the Quantico Marine base in Virginia since May last year.

His lawyers have complained that he is being mistreated by being kept in his cell for 23 hours a day, while the Pentagon says he has to sleep naked and is woken repeatedly during the night to check that he is safe.

"Unfortunately, the U.S. government has not been receptive to a confidential meeting with Mr. Manning," said Mendez in a statement issued from his Geneva office.

Manning's lawyer now understood that the request for a meeting had been refused, added Mendez, a former political prisoner who underwent torture under his country's military dictatorship in the 1970s.

Mendez said he was "deeply disappointed and frustrated by the prevarication" he had met from both State and Defense department officials who made clear they would only allow him to talk to the soldier with a prison official present.

Mendez, an independent expert who reports to the U.N. Human Rights Council, said a monitored conversation would violate his job's requirement for private, confidential and unsupervised interviews with detainees alleging torture and ill-treatment.

The London Guardian newspaper said on Monday more than 250 U.S. legal scholars, including one who taught U.S. President Barack Obama constitutional law and served in the administration, had signed a protest over Manning's "degrading and inhumane" treatment.

Obama has said he has been assured by the Pentagon that the handling of the soldier, an intelligence analyst, was appropriate and met basic U.S. standards.

Last month State Department spokesman P.J. Crowley, a former Air Force Colonel, resigned amid a furor over reports that he said Manning was being held in "ridiculous" conditions.

(Editing by Stephanie Nebehay and Andrew Heavens)