Syria Strike A damaged site in what activists say was a U.S. strike, in Kfredrian, Idlib province Sept. 23, 2014. Photo: Reuters/Abdalghne Karoof

The United States and its regional allies, including Saudi Arabia and the United Arab Emirates, resumed their air campaign against Islamic State group strongholds in Syria, the Pentagon confirmed on Wednesday afternoon. Airstrikes aimed at about 12 targets, including the militant group’s oil installations in Eastern Syria, a U.S. official told CNN.  

“I can confirm that U.S. military and Arab partner forces are undertaking additional strikes today against ISIL terrorists in Syria,” Rear Adm. John Kirby, Pentagon press secretary, said. “These operations are ongoing, so we will not provide additional details at this time. We will do so later as operationally appropriate.”

The airstrikes targeted remote areas of eastern Syria and both east and south of Raqqa, de facto headquarters of the militant group formerly known as the Islamic State of Iraq and Syria, according to CNN’s Barbara Starr.

Admiral Kirby said that precision-guided munitions were used to hit the "modular oil refineries." He said the coalition partners had more aircraft involved in the mission than the U.S. did, and that the 90-minute mission ended with all U.S. and coalition pilots safely returned to their land bases in the region.   

"The 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," according to a Centcom news release. "The destruction and degradation of these targets further limits ISIL's ability to lead, control, project power and conduct operations."

One of the militant group's oil refineries outside of Raqqa’s city center was previously used as an ISIS prison, according to a spokesman for the Raqqa-based activist group “Raqqa Is Being Slaughtered Silently.” Residents in the area did not hear any explosions near the refinery, the group's spokesman told the International Business Times, who could not independently verify this claim.

ISIS gets much of its revenue from seized oil refineries. ISIS revenue numbers vary, but it is estimated that the militants make somewhere between $1 million and $3 million a day from about 10 oil refineries, according to a report released earlier this month from risk-management firm Maplecroft.

The refineries targeted on Wednesday represent only a small amount of the world's oil production. The strikes are unlikely to affect worldwide oil prices -- but will disrupt the terrorists' revenue stream.