An Israeli fighter jet has crashed after it was apparently shot down during airstrikes against "Iranian targets" in Syria.
Israel said its planes struck 12 targets in a "large-scale attack", including three aerial defence batteries and four Iranian targets that are part of Iran's military establishment in the war-ravaged country.
The F-16 crashed during a mission after an Iranian drone had entered Israeli airspace and was shot down, according to the Israeli military.
The Syrian state news agency SANA reported Israel had "carried out a new aggression against one of our military bases in the centre of the country".
"Our air defences repelled it and hit more than one plane."
The Israeli pilots of the crashed F-16 were reported to be alive but one was seriously injured.
Police said the jet crashed in the Jezreel Valley in northern Israel.
An Israeli military statement said: "During the attack, multiple anti-aircraft missiles were fired at IAF (Israel Air Force) aircraft.
"The pilots of one of the aircraft abandoned as per procedure. The pilots landed in Israeli territory and were taken to the hospital for medical treatment."
An Israeli military spokesman said early assessments of the plane's wreckage suggest it was shot down but this has not been confirmed.
The Syrian regime's allies Russia and Lebanese militant group Hezbollah deny claims the Iranian drone entered Israeli airspace, calling them "lies". Iran has also dismissed Israel's claims.
During the attack, anti-aircraft missiles were fired towards Israel, triggering alarms that were heard in northern Israel.
The exchange of fire was the most serious between arch enemies Israel and Iran since the start of the civil war in Syria in 2011.
It marked the first time Israel publicly acknowledged attacking what it identified as Iranian targets in Syria since war broke out.
Moments ago, IAF aircraft, targeted the Syrian Aerial Defense System & Iranian targets in Syria. 12 targets, including 3 aerial defense batteries & 4 Iranian military targets, were attacked. Anti-aircraft missiles were fired towards Israel, triggering alarms in northern Israel
— IDF (@IDFSpokesperson) February 10, 2018
IDF has targeted the Iranian control systems in Syria that sent the #UAV into Israeli airspace. Massive Syrian Anti-Air fire, one F16 crashed in Israel, pilots safe. #Iran is responsible for this severe violation of Israeli sovereignty. Event ongoing, more to follow.
— Jonathan Conricus (@LTCJonathan) February 10, 2018
Israeli security personnel guard the remains of an Israeli F-16 fighter near Harduf, Israel. Picture by: JINI/Xinhua News Agency/PA Images
The Israeli military issued a warning to Tehran, saying it was responsible for the drone that entered Israel.
In recent weeks, Israel has repeatedly warned against the presence of Iranian forces in neighbouring Syria.
Israel has carried out dozens of air strikes on the Syrian armed forces and their allies since the civil war started.
Iran along with Russia is the main military backer of the Damascus government.
Israel has largely confined its operations to targeting Hezbollah, the Shia militant group that is a key ally of Iran.
Israeli military spokesman Jonathan Conricus said Iran was "playing with fire" by infiltrating Israeli airspace and would pay a heavy price.
He said: "We are willing, prepared and capable to exact a heavy price from anyone that attacks us, however we are not looking to escalate the situation.
"This was a defensive effort triggered by an Iranian act of aggression and we are defending our airspace, our sovereignty and civilians."
He said the unmanned aircraft Israel shot down was "on a military mission sent and operated by Iranian military forces".
Mr Conricus said that in response, Israel destroyed the Iranian site in central Syria that launched the drone.
Further attacks were carried out against four additional Iranian targets and eight Syrian sites.
It marks Israel's most significant involvement in Syria to date and the military says it is "ready for various scenarios and will continue to act according to situation assessments".
Iran accused Israel of "lies" and said Syria had the right to "legitimate self-defence" in response to air strikes.
Foreign ministry spokesman Bahram Ghasemi said: "Iran believes Syria has the right to legitimate self-defence. To cover their crimes in the region, Israeli officials are resorting to lies against other countries.
"The allegations regarding surveillance by an Iranian drone are too ridiculous for words."
Iran released a joint statement alongside the other main allies of the Syrian regime, Russia and Lebanese militant group Hezbollah, vowing a "relentless response" to Israeli "aggression".
The statement said the Israeli air strikes had targeted drones used in the fight against "terrorist organisations" especially Islamic State.
Mr Ghasemi added: "Iran does not have a military presence in Syria, and has only sent military advisers at the request of the Syrian government.
"The government and Syrian army are only defending themselves against Israeli aggression."
Lebanon also criticised the Israeli strikes and vowed to write a letter of protest to the United Nations over the use of its airspace for the raids.