President Trump took to Twitter late Sunday to urge Iran to release the retired FBI agent who had been missing in the country since 2007 and said it would be a very positive step toward easing tensions between the two countries since provocations on the Strait of Hormuz.

Robert Levinson’s disappearance has been the source of intrigue. He vanished during an unauthorized CIA mission. Iran acknowledged on Sunday that there is an open Revolutionary Court case involving Levinson.

“If Iran is able to turn over to the U.S. kidnapped former FBI Agent Robert A. Levinson, who has been missing in Iran for 12 years, it would be a very positive step,” Trump tweeted.

If Levinson is alive, he would be the longest-held prisoner in U.S. history.

Last week, Secretary of State Mike Pompeo announced the State Department would offer $20 million on top of a $5 million reward already posted for information leading to Levinson’s recovery and return.

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The AP revealed in 2013 that Levinson-- at 58-- had been on a mission for CIA analysts who had no authority to run spy operations. Levinson’s family had received a $2.5 million annuity from the CIA in order to stop a lawsuit revealing details of his work, while the agency forced out three veteran analysts and disciplined seven others.

Fox News' Brie Stimson and the Associated Press contributed to this report