Between $500 million and $800 million in cash from ISIS funds has been destroyed in airstrikes, a US military official says.

In a briefing to reporters, Maj. Gen. Peter Gersten, who is based in Baghdad, said the US had repeatedly targeted stores of the group’s funds.

The blow to ISIS’ financing has contributed to a 90% jump in defections and a drop in new arrivals, he said.

In 2014, the US Treasury called ISIS “the best-funded terrorist organization” it had encountered.

Maj. Gen. Peter Gersten, the deputy commander for operations and intelligence for the US-led operation against ISIS, said under 20 air strikes targeting the group’s stores of money had been conducted.

He did not specify how the US knew how much money had been destroyed.

In one case, the general said, an estimated $150 million was destroyed at a house in Mosul, Iraq.

Forces fighting ISIS received intelligence indicating in which room of the house money was stored. The room was then bombed from the air, he said.

While it was difficult to know precisely how much money had been destroyed in total, estimates put the figure at between $500 million and $800 million, Maj. Gen. Gersten said.

ISIS’ exact wealth is not known, but, after seizing oil fields and setting taxes, it approved a budget of $2 billion and predicted a $250 million surplus in 2015.

Since then, however, ISIS has lost territory, and its oilfields have been targeted in air strikes by the US-led coalition.

US intelligence indicated ISIS’ cash troubles had led it to start selling vehicles to make money.

The number of those arriving to fight for Islamic State in Iraq and Syria had fallen to about 200 a month, Gen. Peter Gersten said, down from a peak of between 1,500 and 2,000 per month a year ago.

In February, the White House said it believed there were some 25,000 people fighting for ISIS, down from close to 31,500 in 2015.