Airstrikes have destroyed 168 Islamic State oil tanker trucks in eastern Syria, the U.S.-led coalition said in a statement Friday.

The attacks on Thursday near the ancient city of Palmyra were the largest to date, the military said. It added that the strikes resulted in the loss of an estimated $2 million in revenues for the militant group.

“The coalition continues to forcefully prosecute the air war on ISIL revenue capability,” coalition spokesman Col. John L. Dorrian said using an acronym for the Islamic State. “When ISIL has access to large sums of money, they use it to conduct violent terror attacks against anyone who doesn’t share their barbaric ideology.”

Syrian government forces retook Palmyra from the militants in March, but sporadic fighting has continued near the city. Since the start of this year, the extremists have gradually been driven back from many areas in Syria and Iraq which they captured in a lightning campaign in 2014.

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