Israel seized the Golan Heights from Syria in 1967.
This is the second time the Israel Air Force has shot down a Russian-made Syrian jet since 1985.
"Our aerial defense systems identified a Syrian Air Force jet that took off from the T-4 Syrian Air Force base and penetrated Israeli territory", Netanyahu stated. "We will not accept any such penetration of, or spillover into, our territory, neither on the ground nor in the air".
Israel rebuffed on Monday a new Russian offer to keep Iranian forces in Syria away from the Golan Heights ceasefire line, an Israeli official said, complicating Moscow's bid to stabilize the country as the civil war there wanes. A United Nations observer post could be seen just on the other side of the fence.
But with President Assad's men closing in on jihadist groups on the Syrian side of the zone - and pictured reportedly hundreds of metres from an Israeli observation post - Israel has been ratcheting up its rhetoric.More news: Search for Iowa college student continues after she vanished on a jog
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The IDF added, "Since this morning, characteristics of internal warfare appeared in Syria, including growing activity by Syrian air forces". Seven Iranian military personnel were killed in that strike.
Addressing the Security Council's monthly meeting on the Middle East, Danon said the IDF observed the plane "crossing the border.... we tried to contact a few times, and there was no response". He said they did not know if it had deliberately crossed into Israel. The plane crashed inside Syria.
The army radio report said the condition of the pilot was unclear. But Syria's state-run news agency denied this, and accused Israel of targeting a fighter jet over Syrian airspace. He did not elaborate. Both pilots ejected and were injured, one critically.
Reuters cited an Israeli official as saying that while Russian Federation was "committed" to its offer, Netanyahu rejected it and told Lavrov: "We will not allow the Iranians to establish themselves even 100 kilometers from the border" because Iran has long-range missiles that can reach Israel from Syria.
The Israeli military has carried out more than 100 airstrikes in Syria in an effort to prevent Iranian entrenchment or the transfer of arms to its proxy, Hizbollah, and the jet downing was a reminder of the potential for escalation.