The four Americans who were part of a prisoner exchange between the U.S. and Iran have been released by Iran, a senior administration official confirms, and those who wished to depart the country have left.

A fifth American was released separately from the exchange.

The release of the prisoners was the result of "tireless" work by American diplomats, on the sidelines of nuclear negotiations with Iran, President Obama said Sunday.

"I've met with some of the families. I've seen their anguish — how they ached for their husbands and sons," Obama said.

"After the nuclear deal was completed, the discussions between our governments accelerated. Yesterday, the families finally got the news that they were waiting for."

Three of the prisoners — Jason Rezaian, Amir Hekmati and Saeed Abedini — left Iran Sunday morning, and the State Department confirmed they landed in Germany later that day.

The publisher of the Washington Post says in a statement that Jason Rezaian, the journalist who was the Tehran bureau chief for the Post, is accompanied by his wife:

"Friends and colleagues at The Washington Post are elated by the wonderful news that Jason Rezaian has been released from Evin Prison and has safely left the country with his wife, Yeganeh Salehi."We are relieved that this 545-day nightmare for Jason and his family is finally over. We are pleased to see that Iran released four other Americans, and our hope is that those who remain held will soon follow."

Rezaian's family said in a statement that his release "has brought indescribable relief and joy to our family – this nightmare is approaching an end. We are also overjoyed to hear that other Americans being held in Iran also will soon be reunited with their families. Today is an incredible day for all of us."

Rep. Dan Kildee, who represents the family of former marine Amir Hekmati and advocated for Hekmati's release, said in a statement that Hekmati "is coming home."

"I am overcome with emotion that after four and a half years, this terrible ordeal is ending and the Hekmati family will soon be reunited with Amir," Kildee said.

Hekmati's family wrote, in a statement posted on Facebook, that they "remain in hopeful anticipation."

"As many of you know, Amir's father is very ill and soon he will embrace his son once more," the family statement said.

The wife of pastor Saeed Abedini, Naghmeh Abedini, tweeted Sunday morning that her husband "finally made it out of Iranian soil."

The fourth prisoner released as part of the exchange, Nosratollah Khosravi, remains a mystery, and his whereabouts are unknown.

The four prisoners were released as part of an exchange which included the release of seven Iranians and Iranian-Americans in U.S. custody. The U.S. also stopped pursuing 14 Iranians for whom they had been seeking extradition.

American writer and researcher Matt Trevithick was released separately from the prisoner swap, and has reportedly left Iran.

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