White House Spokesperson Jay Carney
White House Spokesperson Jay CarneyWhite House

The White House has appealed to Iran for help in locating a US citizen who recently became the longest-held American hostage in US history, along with two other Americans known to be held by the Islamic regime.

Former FBI agent Robert Levinson was apparently working as a private detective when he went missing during a business trip to Iran's Kish Island in March 2007. Levinson was said to have been investigating cigarette counterfeiting when he was apparently abducted, though it has never been revealed who the kidnappers are or what they want.

He was 64 when he was kidnapped and on Tuesday surpassed the 2,454 days which American journalist Terry Anderson spent in captivity in Lebanon, securing him the dubious record.  

His family have since publicized a video (see below) and several pictures of him which were sent to them in 2010, in which his captives mock the US government and its foreign policy.

The Iranian government for its part has denied holding Levinson, or indeed of having any knowledge of who is. 

But CBS News correspondent and former FBI deputy director John Miller pointed to an interview given by former Iranian President Mahmoud Ahmadinejad to the outlet in September 2012, which he said provided a "tacit admission that he's in their custody and that there have been talks".

During the interview Ahmadinejad did not deny that the Iranian government was holding the American, and said that Iranian and US intelligence agents had met to discuss the issue and that "I thought they'd come to an agreement".

According to CBS News, despite Tehran's denial of any involvement, Levinson's plight was discussed during the recent negotiations over Iran's nuclear program.

And as the American holiday of Thanksgiving approaches, Washington has joined his family in publicly appealing to Tehran to secure his release.

"Today, Mr Levinson becomes one of the longest held Americans in history," said White House spokesman Jay Carney Tuesday.

"As we approach the upcoming holiday season, we reiterate the commitment of the United States Government to locate Mr Levinson and bring him home safely to his family, friends, and loved ones.

"We respectfully ask the government of the Islamic Republic of Iran to assist us in securing Mr Levinson's health, welfare, and safe return."

In addition, the US has requested the release of two American citizens confirmed as being in Iranian custody: Saeed Abedini, a Christian pastor - who was jailed for his religious beliefs - and former US marine Amir Hekmati.

"TheUS government has made a respectful request of the Iranian regime during this holiday season to consider on humanitarian grounds releasing these three Americans, or at least releasing the two Americans we know are detained and locating the whereabouts of the third, Mr. Levinson," said White House spokesman Josh Earnest at a press conference on Tuesday.