Islamic State militants launched an attack overnight against the last major Syrian military air base in the eastern province of Deir el-Zor, activists said Thursday, Dec 4, according to the Associated Press.

The Local Coordination Committees activist collective and the Britain-based Syrian Observatory for Human Rights both reported the fighting for the airfield, which is just outside of the city of Deir el-Zor on the Euphrates River.

The Islamic State group already controls almost the entire surrounding province as part of its self-declared proto-state in Syria and Iraq.

The heavy clashes began with a suicide bombing on a Syrian military position near the air base, the Observatory said, adding that at least 19 government troops and seven IS militants have been killed in the fighting.

The Local Coordination Committees and the Observatory, which relies on a network of activists on the ground, both reported heavy clashes and government shelling on the villages surrounding the airfield.

This summer, IS militants captured a series of Syrian government military bases outside the northeastern city of Raqqa, giving them full control of the entire province by the same name. The extremists killed hundreds of Syrian troops captured in those battles, shooting many in mass killings while beheading others and parading their bodies through IS-held towns and cities.