The U.S. delayed delivering a controversial $400 million payment to Iran until American hostages held there were "wheels up," the Wall Street Journal reported Wednesday.

The revelation adds to mounting criticism that the Obama administration's January payment was for ransom.

The administration has claimed that the timing of the payment, which occurred just as the Islamic Republic released three American hostages, was coincidental, and that the $400 million represents the first installment of a decades-old $1.7 billion arms deal between the Islamic Republic and the U.S. gone awry.

Officials have refused to discuss the details of the cash transfer, including how it was made and the timing of it, despite inquiries from lawmakers and the media.

The Journal reports:

U.S. officials wouldn't let Iranians take control of the money until a Swiss Air Force plane carrying three freed Americans departed from Tehran on Jan. 17, the officials said. Once that happened, an Iranian cargo plane was allowed to bring the cash back from a Geneva airport that day, according to the accounts. … The use of an Iranian cargo plane to move pallets filled with $400 million brings clarity to one of the mysteries surrounding the cash delivery to Iran first reported by The Wall Street Journal this month. Administration officials have refused to publicly disclose how and when the cash transfer authorized by Mr. Obama took place. Executives from Iran's flagship carrier, Iran Air, organized the round-trip flight from Tehran to Geneva where the cash—euros and Swiss francs and other currencies stacked on shipping pallets—was loaded onto the aircraft, these people said. "Our top priority was getting the Americans home," said a U.S. official. Once the Americans were "wheels up" on the morning of Jan. 17, Iranian officials in Geneva were allowed to take custody of the $400 million in currency, according to officials briefed on the exchange. … One of the Americans released in January as part of the prisoner exchange, a Catholic pastor named Saeed Abedini, said he and other American prisoners were kept waiting at Mehrabad airport for more than 20 hours from Jan. 16 to the morning of Jan. 17. He said in an interview that he was told by a senior Iranian intelligence official at the time that their departure was contingent upon the movements of a second airplane. Mr. Abedini said he was asked to testify next month before the House Foreign Relations Committee. State Department officials have rebutted Mr. Abedini's comments, saying the delay in his plane's departure wasn't related to a second plane or the payment of the $400 million. They said the delay was solely tied to U.S. efforts to locate the wife and mother of another imprisoned American, the Washington Post's former Tehran bureau chief, Jason Rezaian, and ensuring they were allowed to board the Swiss plane as well.

Read more at the Journal.