Syria's military said it shot down an Israeli warplane and a drone early Tuesday in response to an attack on Syrian army positions -- a claim denied by Israel.

"Our air defences blocked the attack and shot down the military aircraft in (the southern province of) Quneitra and a drone" in the province of Damascus, said the Syrian army statement carried by state news agency SANA.

It accused Israeli forces of supporting "armed terrorist groups" in the country's south.

The Israeli army said none of its aircraft had been downed.

"Overnight two surface-to-air missiles were launched from Syria after the (Israeli) mission overnight to target Syrian artillery positions," military spokesman Arye Shalicar said.

"At no point was the safety of (Israeli) aircraft compromised. Nothing true about what they claim."

The Israeli military earlier said it targeted Syrian army positions after stray fire from its war-torn neighbour hit the Israeli-held zone of the Golan Heights on Monday.

An Israeli military spokeswoman told AFP Monday's projectile was most likely not intentional, rather spillover from "internal fighting in Syria."

It was the fourth such incident in nine days, and came as a new Syrian ceasefire brokered by Russia and the United States came into force on Monday.

The initial 48-hour truce does not apply to areas held by jihadists such as the Islamic State group.