The United States on Monday urged Tehran to secure the release of former FBI agent Bob Levinson on the 13th anniversary of his disappearance from an Iranian island during an investigation. Mr Levinson, 71, went missing from the resort island of Kish on March 9, 2007, after meeting a contact believed to have insight into the workings of the Iranian government. He is the longest-held US hostage in Iran. After his disappearance, the family received emails from an unidentified terrorist group demanding changes to US policy and threatening his life. The family was sent a video in 2010 and photos in 2011 showing him bound by chains and wearing an orange jumpsuit. The FBI said the “only credible evidence” of responsibility for his abduction pointed to the Iranian regime. Donald Trump’s National Security Adviser, Robert O’Brien, said it was “time for Iran to act” over the case after repeated appeals from the US government for news of his detention and his immediate release. Rewards of $25 million have been offered for his return. “On the 13th anniversary of Bob Levinson’s capture, he and his family are in our thoughts and prayers,” said Mr O’Brien in a tweet released by the US National Security Council. The anniversary comes as US Congress prepares to debate a proposed new law in the name of Mr Levinson that is designed to help hostages and punish those responsible for holding them. One of the requirements is an annual report detailing which of the estimated 3,000 American citizens detained around the world are unlawfully or wrongfully held. “It’s a bill that would consolidate and require a whole-government approach to the issue of hostages and unlawfully imprisoned Americans,” said Jared Genser, an international human rights lawyer who has worked with the families of hostages. Iran has consistently denied any involvement in the disappearance of Mr Levinson but for the first time last year acknowledged that it had an open case before its Revolutionary Court. In a filing to the United Nations, Iran said the case was “on-going” but did not elaborate. Mr Levinson, who had worked for 28 years for the FBI and Drug Enforcement Agency, had been said to be investigating a tobacco smuggling operation and flew from Dubai to Kish the day before he went missing. The Associated Press reported in 2013 that he was on an unauthorised CIA mission to investigate the Iranian government. The family went to court last year to accuse the regime of unlawful hostage taking and torture. In the video released to his family, Mr Levinson, a father-of-seven, wearing a loosely fitting white top, urged the US government to act to help him return home. The video showed a gaunt and emotional Mr Levinson saying that he had been held for three-and-a-half years but was running out of medicine for his diabetes. “I am not in very good health,” he said. “I have been treated well, but I need the help of the US government to answer the requests of the group that has held me for three-and-a-half years.” He added: “Thirty-three years of service to the United States deserves something. Please help me.”