(Reuters) - Israel's military said it shot down a Syrian warplane over the Golan Heights on Tuesday, in the first such incident in three decades.

"It was a Russian-made Sukhoi," a military spokesman said.

Israeli military sources said the plane apparently crossed by accident into Israeli-controlled airspace over the Golan Heights - where fighting from Syria's civil war has spilled over occasionally - and was not on a mission to attack Israeli targets.

The aircraft was intercepted by a U.S.-manufactured Patriot missile, the spokesman said.

Israel Radio said the warplane was apparently carrying out a mission against Syrian rebels battling the forces of President Bashar al-Assad. Israel's military said it shot down a Syrian drone over the Golan Heights on Aug. 31.

Israel last downed a manned Syrian aircraft in 1985, when Israeli fighters on a surveillance mission over Lebanon destroyed two Syrian MiG-23s that approached them.

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OCCUPIED JERUSALEM: Israel shot down a Syrian fighter jet over the Golan Heights Tuesday, the army said, indicating that it had crossed the cease-fire line into the Israeli-occupied sector.

It was the most serious incident to take place on the strategic plateau since the outbreak of the Syrian civil war in 2011.

"A warplane that penetrated Israeli territory was successfully shot down a short while ago by the air defence systems along the Syrian border," a military statement said, without giving further details.

Army radio said it was apparently a MiG-21 fighter jet which was shot down by a surface-to-air Patriot missile, with the wreckage landing on the Syrian-controlled side of the plateau.

The downing came just three weeks after Israel shot down a drone over the Golan as heavy fighting raged on the Syrian side, most of which has been seized by rebels fighting to overthrow President Bashar Assad.

The Assad regime has been hitting back with frequent air strikes in a bid to retake control of the plateau. Some have been close to Israeli positions.

Since the uprising erupted more than three years ago, the plateau has been tense, with a growing number of rockets and mortar rounds hitting the Israeli side, most of them stray, prompting occasional retaliatory fire.

But there have been several incidents of intentional fire, one of which killed an Israeli teenager in June.

Israel seized 1,200 square kilometres (460 square miles) of the Golan during the Six-Day War of 1967, then annexed it in 1981 in a move never recognised by the international community.

Some 510 square kilometres of the Golan remain on the Syrian side of the cease-fire line, with U.N. forces overseeing a buffer zone stretching some 70 kilometres (45 miles) from Lebanon in the north to Jordan in the south.

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