Israel has struck 12 Syrian and Iranian targets in Syria, including an aerial defence system, the country's military has claimed.
The raids, which mark a dramatic escalation of tension in the region, came a few hours after Israel allegedly shot down an Iranian drone that infiltrated the country.
The Israeli military called the drone infiltration a "severe and irregular violation of Israeli sovereignty" and said Iran was "playing with fire".
In a tweet, the Israel Defense Forces said it would "act determinately against such severe violations of Israeli sovereignty" and is "ready for various scenarios".
The IDF will act determinately against such severe violations of Israeli sovereignty by Iran and Syria and will continue to act as necessary.
The IDF is ready for various scenarios and will continue to act according to situation assessments.
— IDF (@IDFSpokesperson) February 10, 2018
But a spokesman later said the country was “not looking to escalate the situation".
He described the air strikes as a “defensive effort triggered by an Iranian act of aggression".
The Israeli military said two of its pilots had been injured - one seriously - when their F-16 jet involved in one of the raids crashed in northern Israel after facing heavy anti-aircraft fire from Syria.
According to the Israeli military, the unmanned aircraft shot down inside Israeli territory early on Saturday was "on a military mission sent and operated by Iranian military forces". The military claims to have the drone in its possession.
IDF spokesman Jonathan Conricus says that in response Israel destroyed the Iranian site in central Syria that launched it. Subsequent attacks were carried out against four additional Iranian targets and eight Syrian sites.
According to the British-based Syrian Observatory for Human Rights, the first of two separate and successive waves of air strikes targeted the central desert area where Syrian troops and their Iranian-backed allies including Hezbollah are known to maintain bases.
It cited unconfirmed reports of casualties among Syrian government forces and allied militiamen.
The Observatory, which monitors the Syria war through a network of activists on the ground, said the second round targeted outposts in the southwestern suburbs of Damascus.
The Israeli military claimed that three aerial defence batteries and four Iranian military sites were among the 12 targets. Anti-aircraft missiles were fired towards Israeli jets triggering sirens across northern Israel, according to the military.
Syrian state TV quoted a military official who described the raids as a "new aggression". He also claimed that Syrian air defences hit more than one Israeli plane.
Israeli Defense Minister Avigdor Lieberman was convening the top brass at military headquarters in Tel Aviv to discuss a further response.
Israel has previously shot down several drones that tried to infiltrate its territory from Syria. Saturday's raids on Iranian sites in response marks an escalation in the Israeli retaliation, however.