Activists say Islamic State fighters have captured a major military air base in northeastern Syria, eliminating the last government-held outpost in an area dominated by the extremist group.

The Britain-based Syrian Observatory for Human Rights says the jihadis broke through the Tabqa air field's defenses Sunday and routed the government forces.

Observatory director Rami Abdurrahman says some army troops also withdrew from the base, and the Islamic State group is now in full control of the facility.

The SANA state news agency confirmed that the government had lost the air base, saying troops "are successfully reassembling after evacuating the airport."