Israel's strikes on Syria last night saw 28 planes take part in raids with a total of around 60 missiles fired, Russia's defense ministry said on Thursday.
"28 Israeli F-15 and F-16 aircraft were used in the attack, which released around 60 air-to-ground missiles over various parts of Syria. Israel also fired more than 10 tactical ground-to-ground missiles," the ministry said in a statement, quoted by Interfax news agency.
At least 23 fighters, including five Syrian regime troops and 18 other allied forces, were killed in the attacks, the anti-Assad Syrian Observatory for Human Rights said Thursday.
The Britain-based observatory said the regime troops killed in the strikes included an officer, adding that the other casualties included Syrians and foreigners.
A Russian deputy foreign minister called for "restraint on all sides" on Thursday, and said Moscow was "concerned" at the escalation.
"We have established contacts with all parties and we call for restraint from all parties," deputy foreign minister Mikhail Bogdanov said, adding that Moscow was "concerned" at the development.
Israel's army said Thursday it had hit dozens of Iranian military targets around Syria in one of its largest military operations in recent years and its biggest such assault against Iranian targets.
The strikes came a day after Israeli Prime Minister Netanyahu held talks in Moscow with Russian President Vladimir Putin, whose country has provided massive military and diplomatic backing to the Assad regime in Syria.
Putin has expressed "deep concern" over US President Donald Trump's withdrawal from the Iran nuclear deal. On Wednesday the Russian leader called the situation in the Middle East "unfortunately very acute."
Netanyahu had told Putin that "it is the right of every state, certainly the right of Israel, to take the necessary steps in order to protect itself from (Iranian) aggression)", his office said in a statement Wednesday, referring to Iran's presence in Syria.
Israel carried out the raids after it said around 20 rockets were fired from Syria at its forces in the Golan Heights at around midnight.
It blamed the rocket fire on Iran's Al-Quds force, adding that Israel's anti-missile system intercepted four of the projectiles while the rest did not land in its territory.
The incident came after weeks of rising tensions and followed US President Donald Trump's decision to withdraw from a key 2015 Iran nuclear deal on Tuesday, a move Israel had long advocated.