A former FBI officer who disappeared in mysterious circumstances in Iran four years ago has been held by the country’s Revolutionary Guard, the cables suggest.

Robert Levinson vanished in 2007 while working as a private investigator on Kish Island, a popular tourist resort in the Persian Gulf. Since then the Tehran regime has rebuffed all efforts from his family to discover his fate, insisting it has no information.

But testimony from a political prisoner who managed to flee the country casts doubt on the official Iranian line and indicates that Mr Levinson may have spent time in one of the Revolutionary Guard’s notorious secret jails.

The informant, who was detained in August 2009 amid the civil unrest sparked by the country’s disputed presidential elections, claims that he saw the words “B. LEVINSON” written on the frame of his cell, beneath three lines of English which he assumed to be a “plea for help”.

The American diplomat who interviewed the source two months later wrote to Washington: “He said that at the time he did not know who Levinson was and only after his release did he use the search engine Google to find that Levinson was a missing American citizen.”

While unable to provide information on the American’s current whereabouts, the prisoner painted a bleak picture of conditions in the Tehran jail, which he described as having a “smell of blood”.

During his four-day ordeal, the source claims that guards burned him with cigarettes and subjected him to sexual assaults.

The US is generally sceptical of information supplied by untested sources, wary of those who concoct false intelligence in the hope of financial reward or assistance with asylum applications.

But the diplomat who interviewed the source noted that he “asked us for no favours” and gave no indication of dishonest motives.

Mr Levinson, who would now be 62, was reportedly investigating a cigarette-smuggling ring when he disappeared in March 2007. The US has always denied he was still working for the FBI.

By Matthew Moore

6:30AM GMT 03 Feb 2011

Find this story at 3 February 2011

© Copyright of Telegraph Media Group Limited 2013