Tabqa airfield – home to several warplane squadrons, helicopters, tanks, artillery, and ammunition bunkers – is the third military base in the area to fall to the extremists since last month. Those victories are part of the Islamic State group’s aggressive push to consolidate its hold on northern and eastern provinces, while also expanding the boundaries of its self-styled caliphate straddling the Syria-Iraq border.

The jihadis launched their long-anticipated offensive last week to seize the sprawling Tabqa facility, located some 45 kilometers (25 miles) from the extremists’ stronghold in the city of Raqqa along the Euphrates River.

After several failed efforts to breach the walls in recent days, Islamic State fighters managed to punch through and storm the air base Sunday, the Britain-based Syrian Observatory for Human Rights said. Government warplanes carried out waves of airstrikes to try to beat back the attack, but those ultimately proved unable to stem the assault.