The US State Department said on Thursday it released $400 million in cash to Iran under a tribunal settlement only once it was assured that American prisoners had been freed and had boarded a plane, Reuters reported.
"The payment of the $400 million was not done until after the prisoners were released," State Department spokesman John Kirby told reporters.
"We took advantage of that to make sure we had the maximum leverage possible to get our people out and get them out safely," Kirby added.
It was the first time the administration has said publicly that it used the payment as leverage to ensure the prisoners were released by Iran.
Three of the five prisoners, including Jason Rezaian, the Washington Posts's Tehran bureau chief; Saeed Abedini, a pastor from Idaho and Amir Hekmati, a former US Marine from Flint, Michigan, as well as some family members, were part of a prisoner exchange that followed the lifting of most international sanctions against Iran following a nuclear deal in 2015.
One more prisoner, Nosratollah Khosravi-Roodsari, chose to remain in Iran, while a fifth prisoner, American student Matthew Trevithick, was released separately.
Both US President Barack Obama and Secretary of State John Kerry have denied that the payment was ransom for the release of the prisoners or tied to the Iran nuclear deal.
The White House announced on Jan. 17 it was releasing $400 million in funds frozen since 1981, plus $1.3 billion in interest owed to Iran, as part of a settlement of a long-standing Iranian claim at the Iran-US Claims Tribunal in The Hague.