One of the American prisoners released from Iran, Jason Rezaian, the Washington Post’s Tehran bureau chief pictured on April 11, 2013.

Three Iranian-Americans left Tehran on Sunday under a prisoner swap following the lifting of sanctions on Iran that is likely to thaw ties further with the United States as Tehran emerges from years of international isolation.

A U.S. official said the Swiss plane had left carrying Jason Rezaian, the Washington Post’s Tehran bureau chief, Saeed Abedini, a pastor from Idaho and Amir Hekmati, a former Marine from Flint, Michigan, as well as some family members.

“Today, our brother, son and friend Amir Hekmati has been released from Iran. We have now been officially told that he is on a plane leaving the country,” Hekmati’s family said in a statement. “It is hard to put into words what our family feels right now. But we remain in hopeful anticipation until Amir is in our arms.”

But one of the four, Nosratollah Khosravi-Roodsari, was not on the plane that left Tehran on Sunday, a senior U.S. official said.

While it was not immediately clear whether he opted to stay in Iran or depart separately, an earlier State Department statement said “those who wished to depart Iran have left.”

Little is known about Nosratollah. According to a report in the Huffington Post, no press coverage could be found about his arrest.

The article went on to state that Obama administration officials had ‘refused to offer any clues about Khosravi-Roodsari’s background, why he was in Iran, or why he had been imprisoned, citing privacy laws.’

A fifth prisoner, the American student Matthew Trevithick, was released separately from the other four on Saturday, a U.S. official said.

“We can confirm that our detained U.S. citizens have been released and that those who wished to depart Iran have left,” a senior U.S. administration official said. Iranian Foreign Minister Mohammad Javad Zarif told CNN as the plane was about to depart.

Several Iranian-Americans held in U.S. prisons after being charged or convicted for sanctions violations have also been released, their lawyers told Reuters on Sunday.

The prisoner deal was the culmination of months of diplomatic contacts, secret talks and legal maneuvering which came close to falling apart because of a threat by Washington in December to impose fresh sanctions on Iran for recent ballistic missile tests.

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