The US-led air war against Islamic State extremists targeted oil refineries in eastern Syria on Wednesday, in a bid to undercut the group's oil smuggling profits, the Pentagon said.
Warplanes from the United States, Saudi Arabia and the United Arab Emirates bombed the oil installations in the latest round of air raids in Syria, the Pentagon said.
Washington expanded its anti-IS air campaign from Iraq into Syria this week, and Wednesday's strikes focused on 12 targets in the east where the IS group controls "small-scale" refineries, the US military's Central Command said in a statement.
A total of 13 air strikes were carried out against the oil refineries and a vehicle, and the initial signs indicated "the strikes were successful."
"These small-scale refineries provided fuel to run ISIL operations, money to finance their continued attacks throughout Iraq and Syria, and an economic asset to support their future operations," Central Command said in a statement.
The oil installations produce between 300 to 500 barrels of "refined petroleum per day," and the destruction of the refineries further limits the IS group's "ability to lead, control, project power and conduct operations."
The Pentagon said Saudi Arabia and the United Arab Emirates played a prominent role in the attack, without providing details.
The targets "were struck with precision-guided missiles by coalition aircraft. In fact, there were more coalition aircraft in the skies on these particular missions than US (planes)," spokesman Rear Admiral John Kirby told CNN.
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The oil facilities hit are located in eastern Syria near al-Mayadin, al-Hasakah, and Abu-Kamal, Central Command said. An IS vehicle that was bombed was located near Dayr-az-Zawr, also in the country's east.
Pentagon officials had initially said oil fields were targeted but later withdrew that account, saying that refineries had been bombed.
The well-funded IS extremists have seized several oil fields in Syria and rudimentary refineries, enabling them to sell smuggled crude oil at cheap prices through intermediaries in Turkey, Iraq, Iran and Jordan.
Analysts say the group operates in a similar manner to a mafia and uses kidnapping ransoms, extortion and robbery -- in addition to oil smuggling -- for its funding.
US intelligence agencies say the IS group takes in at least $1 million a day from its oil sales and other criminal activities.
After IS militants seized large swathes of territory in Syria and Iraq, the United States launched an air campaign against the group in Iraq last month and expanded the strikes into Syria early Tuesday, with five Arab countries -- Bahrain, Jordan, Qatar, Saudi Arabia and the United Arab Emirates -- joining a coalition effort.
US military officers say warplanes from a number of the countries have dropped bombs on IS positions in Syria.
Jordanian aircraft conducted an air strike overnight in Syria, officers said.
The latest air strikes on Wednesday involved a mix of fighter jets and unmanned robotic drones, according to Central Command.