America's relationship with one of its most intractable foes took two giant leaps forward this weekend when Iran released four Americans in a prisoner swap after locking in last summer's nuclear deal and receiving some $100 billion US in sanctions relief.

The announcements culminated a stunning few days of activity for the Obama administration and particularly Secretary of State John Kerry, who led the diplomatic outreach to Tehran at U.S. President Barack Obama's direction through years of slow-grinding negotiations.

Speaking from the White House, Obama on Sunday hailed the "historic progress through diplomacy," long the centrepiece of his foreign policy vision, instead of another war in the Middle East.

Three of the American detainees — Washington Post reporter Jason Rezaian, former U.S. Marine Amir Hekmati and pastor Saeed Abedini — arrived in Germany en route to a U.S. military hospital. They will return home after medical evaluations.

The fourth, Nosratollah Khosravi-Roodsari, opted to remain in Iran, officials said.

United States Iran

Washington Post reporter Jason Rezaian is one of five detained Americans who were released by Iran. (Zoeann Murphy/Associated Press)

The Islamic Republic released the prisoners in exchange for pardons or charges dropped against seven Iranians — six of whom hold dual U.S. citizenship — serving time for or accused of sanctions violations in the United States. A fifth American, student Matthew Trevithick, who had been detained in Iran for roughly 40 days, was released separately.

For all the celebrations, the timing of the deal, finalized hours after Saturday night's United Nations confirmation that Iran made good on pledges to significantly back away from atomic bomb-making capacity, suggested that the Americans possibly were used as pawns by the Iranian government to win long-sought economic relief, as critics allege.

'Problematic deal,' says Ted Cruz

The International Atomic Energy Agency's declaration unlocked some $100 billion US in frozen Iranian assets overseas, and potentially even greater economic benefits through suspended oil, trade and financial sanctions by the U.S. and European Union.

Critics of Obama's Iran policy at home and abroad pounced on the details of the prisoner exchange and the new economic opportunities being afforded Tehran while it still supports Syrian President Bashar al-Assad's government and the militant groups Hamas and Hezbollah.

"This deal is a problematic deal, and it reflects a pattern we have seen in the Obama administration over and over again of negotiating with terrorists, and making deals and trades that endanger U.S. safety and security," Texas Sen. Ted Cruz, a Republican presidential candidate, said on Fox News Sunday.

Nevertheless, the back-to-back breakthroughs reflected painstaking diplomacy by Kerry and administration officials.


Iran will immediately have more money to pay for imports, as the government gains access to tens of billions of dollars of its assets that were frozen abroad by the sanctions. (Raheb Homavandi/Reuters)

The efforts were beset by several hitches, including the detention of 10 U.S. sailors by Iran last week in the Persian Gulf and U.S. plans in late December to impose new sanctions on Iran for ballistic missile testing.

The sailors were released after Kerry's intervention with Iranian Foreign Minister Mohammad Javad Zarif. The sanctions were delayed until Sunday, after the U.S. detainees left Iran.

Prisoner negotiations took 1 year

U.S. and Iranian officials hashed out the prisoner exchange over 11 or 12 meetings over a process that took a little longer than a year, sprouting from the even longer set of talks that led to last July's landmark nuclear accord.

Just before Zarif announced the final pact with his European Union counterpart Frederica Mogherini, Kerry raised the issue of the detained Americans.

A photograph of Kerry speaking with Zarif and Iranian President Hasan Rouhani's brother, Hossein Fereydoun, captured the moment.


Iranian Foreign Minister Mohammad Javad Zarif and the High Representative of the European Union for Foreign Affairs and Security Policy Federica Mogherini announced Iran's compliance with the deal at the United Nations building in Vienna on Jan. 16, 2016. (Leonhard Foeger/Reuters)

Things progressed significantly by November, when Iran was included for the first time in a meeting in Vienna on Syria's civil war. Kerry and Zarif met there to discuss the prisoners.

"We actually shook hands thinking we had an agreement," Kerry said. "I thought it was done."

But the deal bogged down in Tehran and never went through.

"So we went back to work," Kerry told reporters on his plane back to Washington late Saturday.

He described the negotiations as difficult, especially as the Iranians made what he said were unacceptable demands. Kerry said the United States made clear it wouldn't release an accused murderer or narcotics offender.

"For a long time, this didn't move because of the people they were asking for," Kerry recalled. "We said, 'No, and no, and no."'

"And believe me, it's hard when somebody says to you, 'Hey, you give us this guy, we let them all out.' And you have to say no. And you know you're keeping people in a not very nice place for the next whatever number of months," he said.

"But there have to be an enforcement of our principles and our standards here. And in the end, we came out in the right place on that."

More progress was made by Kerry's meeting with Zarif on Dec. 18 in New York. By then, American and Iranian teams in Geneva were working hard on the details of the swap.

The U.S. team, led by Brett McGurk, the special envoy for the fight against ISIS, was prepared to release individuals who violated nuclear-related sanctions on Iran, Kerry said. By Saturday night, those sanctions had been rescinded.

"In the end, the president made the call," he said.

Israel remains steadfastly opposed to the Iran deal and any rapprochement with Tehran. Sunni Saudi Arabia has had tension with Iran since executing a Shiite cleric on Jan. 2, which led to a severing of diplomatic ties between the two.