Up to $800m in cash held by so-called Islamic State (IS) has been destroyed in air strikes, a U.S. military official says, BBC News reports.
Maj Gen Peter Gersten, who is based in Baghdad, said the U.S. 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 U.S. Treasury called IS "the best-funded terrorist organisation" it had encountered.
In a briefing to reporters, Maj Gen Gersten, the deputy commander for operations and intelligence for the U.S.-led operation against IS, said under 20 air strikes targeting the group's stores of money had been conducted.
He did not specify how the U.S. knew how much money had been destroyed.
In one case, he said, an estimated $150m was destroyed at a house in Mosul, Iraq.
Forces fighting IS received intelligence indicating in which room of the house money was stored. The room was then bombed from the air, Maj Gen Gersten said.
While it was difficult to know precisely how much money had been destroyed in total, estimates put the figure at between $500m and $800m, he said.
Islamic State's exact wealth is not known, but, after seizing oil fields and setting taxes, it approved a budget of $2bn and predicted a $250m surplus last year.
Since then, however, the group has lost territory, and its oilfields have been targeted in air strikes by the U.S.-led coalition.
