Israel's foreign ministry said Sunday that Hezbollah had "crossed all red lines" with a rocket strike blamed on the Lebanese armed group that killed 12 youngsters on the annexed Golan Heights.
"Saturday's massacre constitutes the crossing of all red lines by Hezbollah. This is not an army fighting another army, rather it is a terrorist organisation deliberately shooting at civilians," the ministry said in a statement.
Iran-backed Hezbollah, which on Saturday claimed multiple attacks on Israeli military positions following a deadly raid on southern Lebanon, has denied responsibility for the strike that hit the Golan Heights town of Majdal Shams.
The foreign ministry said "an Iranian rocket" caused the deaths of "our boys and girls".
"Hezbollah is the only terror organisation which has those (rockets) in its arsenal", it said.
"Israel will exercise its right and duty to act in self-defence and will respond to the massacre."
The military said the rocket attack killed 12 people aged between 10 and 20 years when they were hit on a football field in Majdal Shams, a Druze town where many residents have not accepted Israeli nationality since the Golan Heights was seized from Syria in 1967.
Prime Minister Benjamin Netanyahu, who was returning early from a visit to the United States, vowed that "Israel will not let this murderous attack go unanswered".
He was due to head a security committee meeting later on Sunday, his office said.
Iran warns of 'consequences' of Israeli attacks on Lebanon after Golan strike
Iran on Sunday warned Israel that any new military "adventures" in Lebanon could lead to "unforeseen consequences", following the deadly rocket strike in the Israel-annexed Golan Heights blamed on Tehran-backed Hezbollah.
"Any ignorant action of the Zionist regime can lead to the broadening of the scope of instability, insecurity and war in the region," said foreign ministry spokesman Nasser Kanani.
He added that Israel will be responsible for "the unforeseen consequences and reactions to such stupid behaviour".
Hezbollah has denied responsibility for the rocket fire that Israeli authorities said killed 12 people including children in the Druze town of Majdal Shams.
Kanani accused Israel of pinning the blame on Hezbollah "to divert public opinion and world attention from its massive crimes" in the Gaza Strip, where war has raged since October 7.
He added that Israel "does not have the least moral authority to comment" on the deaths in Majdal Shams, on the Golan Heights which the country has seized from Syria in 1967 and later annexed in a move not recognised by the United Nations.
Iran does not recognise Israel and has made support for the Palestinian cause a centrepiece of its foreign policy since the 1979 Islamic revolution.
The Islamic republic has hailed Hamas's October 7 attack on Israel that sparked the Gaza war but denied any involvement.