The Israeli army said it had shot down a Syrian fighter jet with surface-to-air missiles after the plane infiltrated its airspace.

"A short while ago, two Patriot missiles were launched at a Syrian Sukhoi fighter jet that infiltrated into Israeli airspace," the Israeli Defence Forces said in a statement.

"The IDF monitored the advance of the fighter jet, which infiltrated about two kilometres into Israeli airspace. It was then intercepted by the Patriot missiles."

Israel's Army Radio said the jet may have crashed on the Syrian-held side of the border and the condition of the pilot was unclear.

Syrian state media said Israel targeted the warplane, which it said was hit while conducting raids in Syrian airspace.

It was the first time Israel shot down a manned Syrian fighter jet since 2014.

The army said there had been an increase in "internal fighting in Syria," including involving the air force, since the morning hours.

It said it was on "high alert and will continue to operate against the breach" of a 1974 ceasefire agreement between the two countries.

Israel has been stressing for weeks that it would enforce the ceasefire between it and Syria amid a Russian-backed government offensive in the country's south.

Today's incident comes a day after Israel's air defences fired at Syrian rockets it feared could hit its territory.

Israeli Prime Minister Benjamin Netanyahu also met Russian Foreign Minister Sergei Lavrov in Jerusalem yesterday to discuss the Syrian conflict.

Israel has been on high alert since 19 June, when Syrian government forces launched the Russia-backed offensive to retake Quneitra and Daraa and provinces, adjacent respectively to the Israeli-held section of the Golan and to Jordan.