The Syrian army and allied fighters have driven insurgents from parts of an air base they had seized in the southern province of Sweida, a group monitoring the conflict reported on Friday.

The Syrian Observatory for Human Rights, a UK-based group that tracks the war, said the insurgents had evacuated parts of al-Thala air base taken in an advance on Wednesday.

"There is a rebel retreat," said Rami Abdulrahman, who runs the Observatory. Heavy Syrian army air strikes and reinforcements drafted in from nearby Sweida city had helped repel the rebel advance, he said.