The White House has dismissed claims that the US paid a ransom to Iran in exchange for the release of five American prisoners.
The US also airlifted $400m (£300.3m) worth of cash to Iran at the same time. The Wall Street Journal reported that US officials sent an unmarked cargo plane loaded with Euros, Swiss, Francs and other currencies, suggesting that the payment may have been related to the release of five Americans, which included Washington Post reporter Jason Rezaian.
But White House Press Secretary Josh Earnest denied the link, saying the payment settled a longstanding dispute between the two countries from before the 1979 Islamic Revolution.
Mr Earnest said Republicans who oppose the landmark Iran nuclear deal have used the payment as a means of undermining the accord. "They're struggling to justify their opposition to our engagement with Iran," he said at a White House press briefing.
Normalising relations
After the world's six major powers announced they would lift sanctions against Iran as a part of the implementation of the historic landmark deal, Tehran and Washington also agreed to settle a number of disputes between the two countries.- Iran nuclear deal: Key details
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The then-Iranian government had purchased $400m (£300.3m) in US military equipment before it was overthrown in the 1979 Islamic Revolution.
The Obama administration had agreed to repay Tehran $1.7bn, which included the original payment as well as interest.