Washington - A $400 million cash delivery to Iran to repay a decades-old arbitration claim may be unprecedented in recent U.S. history, according to legal experts and diplomatic historians, raising further questions about a payment timed to help free four American prisoners in Iran.

The money was sent to Iran on Jan. 17, the same day Tehran agreed to release the prisoners. The Obama administration claimed for months the events were separate, but recently acknowledged the cash was used as leverage until the Americans were allowed to leave Iran. Only then, did the U.S. allow a plane with euros, Swiss francs and other foreign currency loaded on pallets to take off in the other direction for Tehran.

“There’s actually not anything particularly unusual about the mechanism for this transaction,” White House press secretary Josh Earnest said this week of the initial cash payment.

But diplomatic historians and lawyers with expertise in international arbitration struggled to find any similar examples.... Read More: VIN