An independent expert for the U.N.-backed Human Rights Council who visited Julian Assange in a London prison says the WikiLeaks founder "showed all symptoms typical for prolonged exposure to psychological torture."

The U.N. human rights office said Friday that Nils Melzer, the special rapporteur on torture, visited Assange on May 9 with two medical experts in examining potential victims of torture and ill-treatment.

Melzer said it was "obvious" that Assange's health had been affected by "the extremely hostile and arbitrary environment" he faced for years.

U.S. authorities accuse Assange of violating the Espionage Act over publication of secret documents. Sweden wants to question him about sexual misconduct allegations.

Assange lived in Ecuador's Embassy in London in 2012 until he was arrested in April after Ecuadorean officials withdrew his asylum status.