This August 9, 2015 U.S. Air Force photo shows an F-16 Fighting Falcon in support of Operation Inherent Resolve.

The U.S.-led effort to fight ISIS extremists in Iraq and Syria has a new focus: bomb the “Daesh cash.”

Daesh – a widely used Arabic abbreviation for ISIS – have been hoarding millions of dollars in local currency and greenbacks across Iraq and Syria, much of it derived from illicit oil sales.

Colonel Steve Warren, a Baghdad-based spokesman for the U.S.-led coalition that has been fighting the ISIS since August 2014, said nine strikes in Iraq and Syria in recent months have led to the destruction of “tens of millions” of dollars of this money.

“Striking these cash collection points hurts this enemy,” Warren told Pentagon reporters in a video call Wednesday.

“They operate on cash; there is no credit in ISIL,” he added, using another alternative name for the group that seized huge regions in Syria and Iraq in 2014 and 2015.

The U.S. military has released videos of air strikes on what it says are cash-collection facilities. In a video of an attack on a building in Mosul earlier this month, vast plumes of what appears to be money can be seen fluttering into the sky following a huge blast.

A coalition strike hit another cash collection facility in Mosul on Monday, Warren said.

Evidence shows this focus on ISIS cash, combined with the continued bombing of oil trucks that ferry illicit oil around Syria, is hurting ISIS’ bottom line, Warren said. He cited press reports saying IS leaders have had to cut their fighters’ salaries by as much as half.

“A combination of taking away their ability to earn money by striking oil and taking away the money they have on hand by striking the Daesh cash really puts the squeeze on them,” Warren said.

Initial estimates are that the number of civilian casualties in the money strikes was less than 10, Warren said.

Under pressure from critics who say the anti-ISIS campaign is moving too slowly, the Pentagon has indicated it is considering a wider array of targets even if these might cause civilian deaths, provided these attacks yield significant gains against ISIS.

“One of the burdens of command is to weigh the military value of a target versus the potential for civilian loss of life,” Warren said.

“These are tough decisions that commanders have to make.”

Pentagon chief Ashton Carter on Wednesday met with defense ministers from several other nations in the anti-IS coalition and said the next phase of operations would target the de facto ISIS capital Raqqa in Syria, and Mosul in Iraq.

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