BEIRUT — Israel said it shot down a Syrian warplane that crossed into the Israeli-occupied Golan Heights on Tuesday, but Damascus said the jet was fired on as it took part in operations against rebels on Syrian territory.

The incident — the first time Israel has shot down a Syrian jet in four years — added new fuel to weeks of tensions in the Golan as Russian-backed forces close in on ground held by rebels fighting President Bashar al-Assad.

The Israeli military said it monitored the advance of the Syrian Sukhoi fighter jet and shot it down with a pair of Patriot missiles after it penetrated Israeli airspace by about 1.2 miles.

"It was shot down and it crashed...most likely in the southern part of the Syrian Golan Heights," Israeli military spokesman Lt.-Col. Jonathan Conricus said. "We do not have any information so far about the pilots. I do not know of any reports of parachutes being spotted, and we do not know if any pilots have been retrieved."

Tuesday marked the first time Syrian government forces reached the border fence with the U.N.'s Disengagement Observer Force at the edge of the Golan Heights. While Israel maintains it is not involved in internal Syrian affairs and will follow a policy of non-interference, it has been watching closely as Syrian forces battle rebels and Islamic State militants next door.

Israel captured the Golan Heights from Syria in 1967. The U.N. deployed a peacekeeping force between the two sides in 1974.

Smoke trails from two Patriot missiles can be seen near the Israeli city of Safed on Tuesday. Reuters

Syrian state media contradicted Israeli version of events, and reported that a Syrian warplane had been targeted by Israel and hit while conducting raids in Syrian airspace.

"The Israeli enemy confirms its support for the armed terrorist groups and targets one of our warplanes, which was striking their groups in the area of Saida on the edge of the Yarmouk Basin in Syrian airspace," the official news agency SANA quoted a military source as saying.

Minutes before the reported shootdown, Syria's state-run Al-Ikhbariya TV was broadcasting footage from the fence demarcating the U.N. buffer zone between Syrian and Israeli forces inside the Golan Heights. A U.N. observer post could be seen just on the other side of the fence.

The camera showed an Israeli post 440 yards away.

Retired Israeli Brig. Gen. Yossi Kupperwasser said Israel was anxious to not become embroiled in the Syrian conflict.

"Israel is not specifically targeted, these are events that have to do with the ongoing war in Syria," he told journalists. "But the war is now focused on the area close to the border, which is why we see more activity that may threaten Israel."

It is the first time government forces have taken up positions along the frontier since an uprising against Assad swept through the country in 2011. Islamic State militants later seized territory from rebels along the frontier region.