A Syrian warplane that Israel's military said it intercepted on Tuesday was shot down over the occupied Golan Heights but may have crashed on the Syrian-held side of the frontier, Israel's Army Radio reported.

The condition of the pilot was unclear, the report said.

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

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

"Since the morning hours, there has been an increase in the internal fighting in Syria, including an increase in the activity of the Syrian Air Force," it added.

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

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

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

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

Israel seized 1,200 square kilometers (460 square miles) of the Golan Heights from Syria in the 1967 Six Day war, in a move never recognized internationally.

Israel has been on high alert since June 19, when Assad regime 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.