Israel fired a guided missile into Syria today in a "warning shot" after mortar fire from fighting between Syrian troops and rebels hit the Israeli-occupied Golan Heights for the second time in four days.
Israel Radio said it was the first direct engagement of the Syrian military on the Golan since the 1973 war.
It highlighted international fears that Syria's civil war could ignite wider regional conflict.
An Israeli military source said troops fired a Tammuz missile towards a Syrian army mortar crew that had launched a shell which overshot the Golan disengagement fence, exploding near a Jewish settlement without causing casualties.
The missile, known internationally as Spike, can be guided to its target by an operator who sees a live video image from an onboard camera in its nose.
There were no reported casualties in what was evidently a demonstration of fire-power.
In an official statement, the Israeli military said soldiers had "fired warning shots towards Syrian areas" but did not mention the missile or its target destination.
"The IDF (Israel Defence Force) has filed a complaint through the UN forces operating in the area, stating that fire emanating from Syria into Israel will not be tolerated and shall be responded to with severity," it said in a statement.
There was no immediate comment from the 1,000-man United Nations Disengagement Observer Force that patrols the area, and no reaction from Syria.
Interviewed by Israel's Army Radio earlier today, Defence Minister Ehud Barak was asked about public warnings he and another senior official issued to President Bashar al-Assad last week to rein in Syrian sweeps against rebels near the Golan.
"The message has certainly been relayed. To tell you confidently that no shell will fall? I cannot. If a shell falls, we will respond," Mr Barak said, without elaborating.
Prime Minister Benjamin Netanyahu, also speaking before today’s mortar strike on the Golan, told his cabinet Israel was "closely following what is happening on our border with Syria .. and (is) prepared for any development".