Israel has struck Iranian military sites in Syria to prevent what it said was a pending drone strike by Iran.
Israel's military rarely acknowledges operations in Syria, but it claimed on Saturday its strikes had prevented an attack on Israel "using killer drones".
PM Benjamin Netanyahu hailed his military's "major operational effort".
Israel is believed to have carried out hundreds of strikes in Syria since civil war broke out there in 2011, to try to prevent Iran gaining a foothold.
An Israeli military spokesman said the strikes on Saturday targeted the Quds Force of the Iran's Islamic Revolution Guard Corps (IRGC) in Aqraba, south-east of the capital, Damascus.
A Syrian military source quoted by the official Sana news agency said that Syrian anti-aircraft defences "detected enemy targets from Golan heading towards the area around Damascus".
"The aggression was immediately confronted and so far the majority of the enemy Israeli missiles have been destroyed before reaching their targets," the source said.
In a tweet, Mr Netanyahu said: "I reiterate: Iran has no immunity anywhere. Our forces operate in every sector against the Iranian aggression. 'If someone rises up to kill you, kill him first.'"
The head of the Iranian-backed Lebanese militant group Hezbollah, Hassan Nasrallah, said two Lebanese nationals had been killed in the Israeli strike, which he said targeted Hezbollah positions.
Separately, reports said two Israeli surveillance drones had come down in the Lebanese capital, Beirut.
Hezbollah officials said an unmanned drone fell on the roof of a media centre belonging to the group, and was followed by a second unmanned drone that exploded in mid-air and crashed nearby.
Hassan Nasrallah denounced the attack, saying that it was the first since the two sides fought a brief war 13 years ago.
The group would prevent any future attacks, he said, adding: "The time when Israeli aircraft come and bombard parts of Lebanon is over."
Residents told the Associated Press they heard a large explosion that shook the area, after hearing the sound of an aircraft. Israel's military declined to comment on the reports.
Lebanese Prime Minister Saad Hariri called Israel's alleged surveillance drones a "blatant attack on Lebanon's sovereignty".
"This new aggression... forms a threat to regional stability and an attempt to push the situation towards more tension," he said in a statement.
Israel reportedly also carried out an airstrike last month on a weapons depot in Iraq. The New York Times, citing unnamed US officials, said that Israel was behind the 19 July strike on an arms depot that the officials said was being used by Iran to move weapons to Syria.
The Israeli military refused to comment on the strike.