A US-led coalition airstrike in Syria hit an oil refinery run by the Islamic State militant group near the border with Turkey on Sunday, killing 30 people, the Syrian Observatory for Human Rights reported.

Rami Abdulrahman, who runs the observatory, said the dead were refinery workers and Islamic State militants. The targeted refinery was just northeast of the town of Tel Abyad near the Turkish border.

Asked about the report, a spokesman for the US Combined Joint Task Force overseeing the fight against Islamic State, said: "When an allegation of civilian casualties caused by U.S. or coalition forces is determined to be credible, a thorough investigation would be launched to determine the accuracy of the claim and any circumstances surrounding it."