U.S. officials wouldn't allow Iranians to take control of $400 million in cash sent to the country earlier this year until three American prisoners had left Iran, according to a new report.

After a Swiss Air Force plane carrying the three Americans left Tehran on Jan. 17, an Iranian cargo plane with the cash was allowed to return from Switzerland, The Wall Street Journal reported Wednesday, citing U.S. officials and others briefed on the operation.

The report is likely to spur new questions from Republicans about the controversial payment. Republicans have accused the administration of paying a ransom to free the detained Americans.

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The White House, though, has denied that the $400 million was a ransom payment to Iran.

The payment, first acknowledged by the administration in January, was part of a $1.7 billion settlement to resolve a dispute from an arms deal from the 1970s. Republicans seized on new details of the exchange earlier this month to blast the nuclear deal between the U.S. and Iran reached last year.

Republican presidential nominee Donald Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE has called the reported exchange a scandal.

President Obama bristled at criticism of the cash transfer earlier this month, saying, "this wasn't some nefarious deal."

U.S. officials have emphasized that the release of the American prisoners and the cash transfer to Iran took place through separate diplomatic channels.

“It’s time for the Obama White House to drop the charade and admit it paid a $400 million ransom to the world’s leading state sponsor of terrorism," Republican National Committee (RNC) Chairman Reince Priebus said in a new statement on Wednesday.

"President Obama has foolishly put a price on the head of every American abroad and it should be no surprise that Iran has since detained more U.S. citizens," Priebus added.