WASHINGTON (AP) — America’s $400 million cash delivery to Iran to repay a decades-old arbitration claim may be unprecedented in recent U.S. history.

Legal experts and diplomatic historians say there are few similar examples.

The money was sent to Iran on Jan. 17, the same day Iran agreed to release a group of American prisoners. The Obama administration claimed for months the events were separate. But the administration recently said it withheld the money as leverage until the prisoners left Iran.

The administration also says the delivery of euros, Swiss francs and other foreign currency in pallets of cash wasn’t unusual.

But asked to recall a similar payment of the U.S. using cash or hard money to settle an international dispute, the office of the State Department historian couldn’t provide an example.