Up to $800m (£550m) in cash held by so-called Islamic State (IS) has been destroyed in air strikes, a US military official says.
Maj Gen Peter Gersten, who is based in Baghdad, said the US had repeatedly targeted stores of the group's funds.
The blow to the group's financing has contributed to a 90% jump in defections and a drop in new arrivals, he said.
In 2014, the US Treasury called IS "the best-funded terrorist organisation" it had encountered.