Story highlights The downed Syrian plane was a Sukhoi-24, an Israeli military spokesman says

IDF: The plane was attempting to infiltrate Israeli airspace in the Golan Heights

Activist group says the plane was targeting sites around the Syrian town of Quneitra

U.N. peacekeepers have left the Syrian-controlled side of the Golan Heights

Israel's military said Tuesday it shot down a Syrian warplane over the Golan Heights amid what it described as growing tensions in the border area.

According to the Israel Defense Forces, the plane "was identified while attempting to infiltrate Israeli airspace in the Golan Heights."

Israel used a Patriot anti-aircraft missile to bring it down, the IDF said.

Military spokesman Lt. Col. Peter Lerner said the aircraft shot down was a Russian-made Sukhoi-24 and that both the pilot and co-pilot ejected into Syria.

The plane penetrated roughly a kilometer (more than half a mile) into Israeli airspace, he said.

Syrian state TV also reported that Israeli forces had shot down a Syrian warplane.

A Syrian fighter jet is in flames Tuesday after being hit by the Israeli military over the Golan Heights.

Defense Minister: We will act strongly

The Syrian Observatory for Human Rights, a London-based activist group, said the Syrian fighter jet was targeting the countryside around the Syrian town of Quneitra, where the only border crossing between Israel and Syria is located.

Militants in the area are trying to dislodge Syrian government forces from their last two strongholds in the area, the group said.

Israeli Defense Minister Moshe Ya'alon said the Syrian fighter jet "came close to Israeli territory on the Golan Heights in a threatening manner, and even crossed the border line."

He said Israel would use whatever means were necessary to protect its citizens.

"We have made it clear, and we are making it clear now as well: We will not allow any factor be it a country or a terror organization, to threaten our security and violate our sovereignty. We will act strongly against all attempts even if it is a mistake or intentional."

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Border area called 'Highly unstable'

An IDF statement posted online said the Israel-Syria border had been "highly unstable" in recent months.

"As the civil war rages in Syria, IDF forces have experienced combat in the region, both from targeted strikes and errant fire," it said.

The incident came as the United States and a number of Arab allies began bombing ISIS targets in the Syrian town of Raqqa, far to the northeast.

U.N. forces withdrew last week from the Syrian-controlled side of the Golan Heights, a little more than two weeks after Islamic militant fighters took some peacekeepers hostage and besieged others.

Al-Nusra Front freed 45 U.N. peacekeepers from Fiji in good condition earlier this month, while forces from the Philippines escaped after exchanging fire with militant fighters, according to media reports.