Israel launched heavy air strikes in Syria on Saturday, saying it hit air defenses and Iranian targets, and the Syrian army claimed to have brought down an Israeli F-16 that crashed in
northern Israel in a major escalation of tension.
The Israeli military said early assessments indicated the jet had been shot down by Syrian fire, but this was still unconfirmed.
It marked the most serious confrontation yet in Syria between Israel and Iranian and Iran-backed forces that have established a major foothold in the country while fighting in support of President Bashar al-Assad in the civil war.
Israel said the F-16 crashed during a mission to strike Iranian drone installations in Syria. It said it sent its jets into Syria after shooting down an Iranian drone over Israeli territory earlier on Saturday.
The military alliance fighting in support of Assad denied any of its drones had entered Israeli air space. In a statement, it said Israel had targeted an air base in the Homs desert that is being used to fly drones in missions against Islamic State.
Such "terrorist action" by Israel would be met with a "severe and serious response," it said.
The Israeli military spokesman said Israel did not seek escalation in the region, calling its action a "defensive effort triggered by an Iranian act of aggression".
Iran's expanding clout during Syria's nearly seven-year-long war, including deployments of Iran-backed forces near the Golan frontier, has raised alarm in Israel, which has said it would act against any threat from its regional arch-enemy Tehran.
Iranian and Iran-backed Shi'ite forces, including Lebanon's Hezbollah, have deployed widely in support of Assad. Iran's military chief warned Israel last October against breaching Syrian airspace and territory.
Israel's air force has targeted Syrian military and Hezbollah targets in Syria on an almost regular basis, but its attacks on Saturday appeared to be the most intense yet.
Referring to the downed Israeli F-16, an official in the pro-Assad alliance said a "message" had been delivered to Israel. "I do not believe matters will develop to a regional war," the official said.