Action beyond hitting the Islamic State's oil revenues with bombs in Syria is needed if the campaign is to succeed, a peace advocacy group said.

In September, U.S. President Barack Obama announced a military campaign to take out militants from the Sunni-led terrorist group in control of parts of Iraq and Syria. Now dubbed Operation Inherent Resolve, the campaign has focused on Syrian oil installations controlled by the group calling itself the Islamic State.

Paul Kawika Martin, director of advocacy group Peace Action, said the military campaign has so far failed to contain IS.

"Instead of methods that are likely to cause more extremism like air strikes to reduce oil revenues, other options include freezing bank accounts of ISIS supporters, negotiating with local villages where oil pipelines are being used and cracking down on the market of cultural artifacts from Syria and Iraq," he said in a statement e-mailed Wednesday to UPI.

IS was said to be generating as much as $2 million per day from illicit oil. Martin said the group may be in control of as much as 80,000 barrels of oil per day, but noted a decline in oil prices since June may be hurting the group's ability to generate revenue.

A report last week from IHS Energy found IS is selling its oil on the black market for about half of the market price.