FOUR YEARS AFTER HE disappeared inside Iran, US officials say they have received proof that a retired FBI agent is still alive.

The AP reports that, until now, the US had lacked reliable information about Robert Levinson since his mysterious disappearance in March 2007 while on the Iranian island Kish.

Although his location and possible captors remain unclear, proof he is alive is a dramatic development in the case.

Iran has repeatedly denied having any information regarding Levinson, but US diplomats and investigators earlier claimed they believed he was taken by Iranian government agents.

Yesterday, the US State Department released a short statement from Hillary Clinton appealing to Iran for assistance in returning Levinson to the US. The nature of the proof Levinson is alive has not been released because US officials fear it may impeded efforts to free him.

Iran’s President Ahmadinejad previously said he had no information about Levinson and accused the FBI of withholding information about why Levinson was in Iran at all.

His family say he was investigating illegal cigarette smuggling after he retired from the FBI in 1998, and that was what brought him to Iran.

- AP