The United States government delivered currency worth $400 million to Iran this past January — at the same time the country was returning four American prisoners to the U.S.

John Kirby, a State Department spokesman, denies the cash transfer was in exchange for the American citizens, but critics are skeptical. The government says the $400 million was the first installment paid in a “$1.7 billion settlement the Obama administration reached with Iran to resolve a failed 1979 arms deal dating from just before the Iranian Revolution,” reports Fox News.

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Claiming that the cash deal and the release of Americans had nothing to do with each other, Kirby said “not only were the two negotiations separate, they were conducted by different teams on each side.”

Despite Kirby’s statement, The Wall Street Journal says U.S. officials are admitting that the Iranian negotiators on the prisoner exchange said they wanted the money to prove they gained something out of the release.

“The Journal also reported that President Barack Obama did not disclose the $400 million cash payment when he announced Jan. 17 that the arms deal dispute had been resolved,” according to Fox News.

While it is unclear exactly how the $1.7 billion was paid, the $400 million sent to Iran was a mixture of euros, Swiss francs, and other currencies because it is illegal for the U.S. to use American dollars with Iran.

For more on the danger of the Iran Deal, click here.