Two Americans in Iran not returning home

TEHRAN, Jan. 17 (UPI) -- Two Americans whom officials believe are still being detained by Iran were not among four others recently returned as part of a prisoner exchange.

On Sunday Tehran said it was not releasing businessman Siamak Namazi, 44, and remained silent about former FBI agent Robert Levinson, 67, according to the Washington Post.

Namazi is an Iranian-American who was arrested in October while visiting a friend in Tehran, where he had reportedly conducted business for the past decade. It was not clear why he was arrested, and his family expressed surprise he was not among four other Americans freed as part of a swap for seven Iranians on Saturday.

Levinson went missing on the Iranian island of Kish in 2007 while working as a CIA contractor. Iranian officials deny any knowledge of his whereabouts, and despite the FBI offering a $5 million reward for information leading to Levinson's return, U.S. officials have said they are unsure if he is still alive.

Voice of America reported Sunday at least three of the four American prisoners -- Washington Post journalist Jason Rezaian, former U.S. Marine Amir Mirzaei Hekmati and Christian pastor Saeed Abedini -- had flown out of Tehran but that Iranian-American businessman Nosratollah Khosravi-Roodsari had not. The U.S. State Department said "those who wished to depart Iran have left."

A fifth American, language student Matthew Trevithick, was released separately on Saturday after being detained since late 2015.

The prisoner swap comes as U.S. Secretary of State John Kerry and other diplomats are working to see through the implementation of a nuclear agreement reached last summer between Tehran and the five permanent members of the U.N. Security Council plus Germany, referred to as P5+1.