Syrian activists say U.S.-led coalition airstrikes hit an oil refinery in northern Syria on Sunday, killing 30 people.

The Britain-based Syrian Observatory for Human Rights, which uses a network of sources throughout Syria to track violence there, said the Islamic State group was operating the refinery, and that the dead included both militants and workers.

The coalition of warplanes supporting Iraq’s military in its push to regain territory from Islamic State fighters has conducted more than 2,300 airstrikes in Iraq and Syria since August, according to data from the U.S. Defense Department.

Those strikes include a recent push to respond to the Iraqi government’s request to help protect the country’s antiquities, which have been targeted for destruction by the militants in recent weeks.

U.N. Secretary-General Ban Ki-moon said in a statement late Sunday he is “outraged” by the destruction of cultural sites, including the UNESCO World Heritage Site at Hatra in northern Iraq.

He called on the international community to help stop such attacks and the illicit trafficking of cultural artifacts.

The ongoing U.S.-led airstrikes have not extended to the week-old offensive by Iraqi forces and Shi’ite militias to retake the city of Tikrit, a key stronghold between government-controlled Baghdad to the south and the Islamic State-held Mosul to the north.

The ground fighting involves thousands of troops with tactical help from Iran.

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