Israel said it had attacked "dozens" of Iranian targets in Syria in response to rocket attacks in the Golan Heights
World powers have called for 'calm on all sides' amid escalating tensions between Israel and Iran in Syria.
Fears that countries could be heading towards a direct war have intensified following a series of attacks over the last 24 hours.
Israel's military earlier said it had attacked "dozens" of Iranian targets in Syria - or almost all of Iran's military infrastructure in the country - in response to about 20 rockets that were fired at Israeli targets in the Golan Heights.
Israeli Defence Forces accused Iranian Quds forces inside Syria of being behind the initial rocket attacks, saying they viewed "this Iranian attack with severity."
The IDF strikes were a response to the rockets that were launched by the Iranian Quds Forces against IDF positions on the Golan Heights & the Syrian aerial defense fire at IAF aircraft— IDF (@IDFSpokesperson) May 10, 2018
The IDF has struck dozens of Iranian military targets in Syria in response to the Iranian rocket attack against Israel. Quds force is behind attack and has played the initial price. IDF remains ready for various scenarios but does not seek to escalate the situation. pic.twitter.com/4rC8gHK2LG— Jonathan Conricus (@LTCJonathan) May 10, 2018
Israeli Prime Minister Benjamin Netanyahu claimed the rocket fire "crossed a red line" and his country had "reacted accordingly".
He said Israel's action was also a "clear message" to Syrian leader Bashar al-Assad - saying that if the Syrian Army acts against Israel, "we will act against it".
The dramatic escalation in the Middle East came less than 48 hours after Donald Trump announced the US was withdrawing from the Iran nuclear deal, and that his country would impose fresh sanctions on the Iranian regime.
In a phone call with Mr Netanyahu, British Prime Minister Theresa May condemned the Iranian rocket attacks, and said the UK supports Israel's right to defend itself.
In a read-out of the call, Mrs May's office added: "The Prime Minister noted our statement calling on Iran to refrain from any further attacks, and for calm on all sides."
The US - a key ally of Israel - also condemned the attacks.
White House Press Secretary Sarah Huckabee Sanders said: "The Iranian regime’s deployment into Syria of offensive rocket and missile systems aimed at Israel is an unacceptable and highly dangerous development for the entire Middle East.
"Iran’s Islamic Revolutionary Guard Corps (IRGC) bears full responsibility for the consequences of its reckless actions, and we call on the IRGC and its militant proxies, including Hizballah, to take no further provocative steps."
Meanwhile, a spokesperson for UN Secretary General António Guterres said: "The United Nations Disengagement Observer Force (UNDOF) has maintained contact with the Syrian Arab Armed Forces and Israel Defense Forces, urging both parties to exercise maximum restraint and abide by their obligations under the Disengagement of Forces Agreement.
"The Secretary-General urges for an immediate halt to all hostile acts and any provocative actions to avoid a new conflagration in the region already embroiled in terrible conflicts with immense suffering of civilians. "
Earlier this week Mr Netanyahu said Israel 'fully supported' President Trump's decision to leave the Iran deal, while European leaders were among those who expressed disappointment over the US withdrawal.
The latest developments in the region come amid the ongoing conflicts in both Syria and Yemen, which have left millions of people displaced.