Five Americans detained for years in Iran walked off a plane and into freedom Monday, some arm-in-arm, as part of a politically risky deal that saw President Joe Biden agree to the release of nearly $6 billion in frozen Iranian assets owed by a third country, South Korea.

The successful negotiations for the Americans’ freedom brought Biden profuse thanks from their families but heat from Republican presidential rivals and other opponents for the monetary arrangement with one of America’s top adversaries.

“Today, five innocent Americans who were imprisoned in Iran are finally coming home,” Biden said in a statement released as the plane carrying the group from Tehran landed in Doha, Qatar. A plane carrying the Americans home to the United States was due to land Monday night.

Iran’s hard-line President Ebrahim Raisi, on hand for the United Nations General Assembly in New York, suggested Monday’s exchange could be “a step in the direction of a humanitarian action between us and America.”

“It can definitely help in building trust,” Raisi told journalists.

However, tensions are almost certain to remain high between the U.S. and Iran, which are locked in disputes over Tehran’s nuclear program and other matters. Iran says the program is peaceful, but it now enriches uranium closer than ever to weapons-grade levels.

The prisoner release unfolded amid a major American military buildup in the Persian Gulf, with the possibility of U.S. troops boarding and guarding commercial ships in the Strait of Hormuz, through which 20% of all oil shipments pass.

After the plane slowed to a stop in Doha, three of the prisoners walked down the stairs. They hugged the U.S. ambassador to Qatar, Timmy Davis, and others.

The three — Siamak Namazi, Emad Sharghi and Morad Tahbaz — then threw their arms over one another’s shoulders and walked off to a building in the airport.