Jerusalem/Beirut: Anti-aircraft fire downed an Israeli warplane returning from a bombing raid on Iran-backed positions in Syria on Saturday in the most serious confrontations yet between Israel and Iranian-backed forces based across the border.

The F-16, one of at least eight Israeli planes despatched in response to what Israel said was an Iranian drone’s incursion into its airspace earlier in the day, was hit by a Syrian anti-aircraft missile and crashed in northern Israel, an Israeli official told Reuters.

Both pilots ejected and were injured, one critically.

Israel then launched a second and more intensive air raid, hitting what it said were 12 Iranian and Syrian targets in Syria, including Syrian air defence systems.

Lebanon’s Iran-backed Hezbollah group said the downing of the plane marked the ‘start of a new strategic phase’ that would limit Israel’s ability to enter Syrian airspace.

Iran’s involvement in Syria in support of President Bashar al-Assad in a nearly 7-year-old civil war - including the deployment of Iran-backed forces near the Israeli-occupied Golan Heights - has alarmed Israel, which has said it would counter any threat.

But Israel and Syria signalled they were not seeking wider conflict, even as Prime Minister Benjamin Netanyahu rushed to military headquarters in Tel Aviv and the pro-Assad alliance pledged a strong response to any Israeli ‘terrorist action’.

‘Israel seeks peace but we will continue to defend ourselves steadfastly against any attack against us or any attempt by Iran to establish itself against us in Syria,’ Netanyahu said in a televised statement.

Russia, whose forces began intervening on behalf of Assad in 2015, expressed its concern and urged both sides to exercise restraint and avoid escalation.

Netanyahu said he had spoken by telephone with Russian President Vladimir Putin and that they agreed Israel-Russia military coordination in regard to Syria would continue.

Putin told Netanyahu in the phone call that there was a need to avoid any steps that would lead to a new confrontation in the region, Interfax news agency reported.

A Western diplomat in the region said: ‘My impression is that it seems to be contained at this point. I don’t think anybody wants to escalate further.’

A Pentagon spokesman said the United States fully supported Israel’s right to defend itself, and a State Department spokeswoman said the United States is ‘deeply concerned’ about the ‘escalation of violence over Israel’s border.’

UN Secretary-General Antonio Guterres is closely watching the ‘alarming’ military escalation throughout Syria and calls on all sides to exercise restraint and work for an immediate and unconditional de-escalation of violence, a UN spokesman said.