You might describe it as a payment in small, unmarked bills. Last January as Iran freed four American hostages held in Tehran, the Obama administration ordered the delivery of $400 million to the Iranian regime without telling the American public, reports The Wall Street Journal.

Wooden pallets stacked with euros, Swiss francs and other currencies were flown into Iran on an unmarked cargo plane, according to these officials. The U.S. procured the money from the central banks of the Netherlands and Switzerland, they said.

The money represented the first installment of a $1.7 billion settlement the Obama administration reached with Iran to resolve a decades-old dispute over a failed arms deal signed just before the 1979 fall of Iran’s last monarch, Shah Mohammad Reza Pahlavi.

The Journal claims to have spoken to American and European officials briefed on the matter as well as congressional staff who were told after the fact. But the Obama administration insists the payment had nothing to do with the hostages, only the failed arms deal, calling the timing coincidental.

“As we’ve made clear, the negotiations over the settlement of an outstanding claim…were completely separate from the discussions about returning our American citizens home,” State Department spokesman John Kirby said. “Not only were the two negotiations separate, they were conducted by different teams on each side, including, in the case of The Hague claims, by technical experts involved in these negotiations for many years.”

But U.S. officials also acknowledge that Iranian negotiators on the prisoner exchange said they wanted the cash to show they had gained something tangible.  

The deal is being denounced by many in Washington including Republican Senator Tom Cotton of Arkansas who says it effectively puts a price on the head of Americans in the region and will encourage more hostage- taking. Others worry the money may have been used to fund terrorists in other areas. Iran is one of the top state sponsors of terrorist groups in the world.