WASHINGTON (AP) – The U.S. military is accelerating its attacks on tanker trucks used by the Islamic State to haul oil for its lucrative smuggling operations.

A U.S. spokesman in Baghdad said Monday that the U.S. hit 283 oil tanker trucks in eastern Syria on Saturday as part of a concerted campaign to cripple the militants’ oil revenues.

U.S. officials say oil accounts for about half of the group’s income.

On Nov. 15, the U.S. began targeting oil tanker trucks by bombing 116 of them. It also is attacking oil facilities.

U.S. Army Col. Steve Warren in Baghdad said it appears no civilians were hurt in Saturday’s attacks. He said U.S. planes chased off the drivers by dropping warning leaflets and making strafing runs in the area prior to bombing the trucks.