The strikes hit two oil areas in Deir el-Zour province a day after the United States and its Arab allies pummelled a dozen makeshift oil producing facilities in the same area near Syria's border with Iraq. The raids aim to cripple one of the militants' primary sources of cash, black market oil sales that the US says earn up to USD 2 million a day.
The Observatory said the strikes were believed to have been carried out by the coalition. Another activist collective, the Local Coordination Committees, also reported four strikes on Mayadeen that it said were conducted by the US and its allies.
The Observatory, which relies on a network of activists inside Syria, said there were reports of casualties in the strikes, but did not have concrete figures.
Also Read
The strikes there targeted another oil production area, as well as vehicles the militants had brought in from Iraq and tried to bury in the ground to protect them, according to Observatory director Rami Abdurrahman.
The US-led coalition, which began its aerial campaign against Islamic State fighters in Syria early Tuesday, aims to roll back and ultimately crush the extremist group that has created a proto-state spanning the Syria-Iraq border. Along the way, the militants have massacred captured Syrian and Iraqi troops, terrorised minorities in both countries and beheaded two American journalists and a British aid worker.
Activists say the militants have cut back the number of gunmen manning checkpoints, apparently fearing more strikes.
There has also been an exodus of civilians from Islamic State strongholds.
Raqqa, an ancient city located on the Euphrates River in northeastern Syria, is the de facto capital of the Islamic State group's self-declared caliphate.