Damascus, Dec 6 (IANS): Syrian troops Saturday halted the advance of the Islamic State (IS) militants near a key military airbase in the country's eastern province of Deir al-Zour, a monitoring group reported.

The advance of the IS toward the airbase came to a halt as a result of the heavy shelling by the Syrian government troops, Xinhua reported citing the Syrian Observatory for Human Rights.

The Britain-based watchdog claimed that the Syrian troops used chlorine gas against the IS militants.

The IS fighters also withdrew from a nearby mountain they previously captured as a result of the shelling by the troops, said the watchdog.

Meanwhile, state news agency SANA cited military sources as saying that the Syrian troops Saturday attacked IS positions in the areas surrounding the airbase, without commenting on the activists' charges of the use of chlorine gas.

In an earlier report Saturday, the observatory said at least 111 combatants of both Syrian government troops and the IS militants had been killed over the past three days of fighting in the vicinity of the airbase.

The death toll includes 51 government troops and 60 IS fighters, 25 of whom were Syrians, said the observatory.