Israel captured the Golan Heights from Syria during the 1967 war and the area was later annexed in 1981. They have now retaliated against Hezbollah after a rocket strike on a football pitch in Golan Heights killed 12 people.
Israel's air force has announced it has hit a number Hezbollah targets in Lebanon.
The move comes after 12 children and young adults were killed in a rocket strike during a game of football in the Israeli-occupied Golan Heights.
Israel was quick to blame the Lebanese militant group for Saturday's strike on the Druze town of Majdal Shams - but Hezbollah has strongly denied any involvement since it happened.
Early on Sunday morning, the IDF explained it had conducted strikes against seven separate Hezbollah targets, claiming they were "deep inside Lebanese territory".
It is not yet clear whether there have been any casualties.
The strike on the football pitch, the deadliest attack on an Israeli target since fighting between the the IDF and Hamas erupted in October, has raised fears of a broader conflagration in the region.
The Iran-backed Lebanese group Hezbollah said it struck a military base in the Golan Heights in retaliation for Israeli attacks on a village in Lebanon, but denied it was behind the strike on the soccer field.
"The Islamic Resistance has absolutely nothing to do with the incident, and categorically denies all false allegations in this regard," the group said in a written statement.
But the Israeli military said that according to intelligence in its possession, "the rocket launch toward Majdal Shams" was carried out by Hezbollah.
"The Hezbollah terrorist organisation is behind the rocket launch at a soccer field in Majdal Shams which caused multiple civilian casualties, including children, earlier this evening," the IDF statement said.
Israel's Prime Minister Benjamin Netanyahu, who has been on an official visit to the United States, said he was bringing forward his return home and vowed a retaliation. He said on X he would immediately convene the Security Cabinet upon his return.
"Hezbollah will pay a heavy price, the kind it has thus far not paid," he said in a phone call with the leader of the Druze community in Israel, according to a statement from his office.
And speaking to local television news Channel 12, Foreign Minister Israel Katz said, "We are facing an all-out war."
Six-Day War of 1967
Israel captured the Golan Heights from Syria during the 1967 war and the area was later annexed in 1981.
It's mainly inhabited by the Arabic-speaking Druze people who were offered Israeli citizenship when the territory was annexed, but most refused.
Around 25,000 Druze live in the Golan Heights.
Israel and Hezbollah have traded near daily fire since the outbreak of the war in Gaza last October.
Over the past weeks, the exchange of fire along the Lebanon-Israel border intensified with Israeli airstrikes and rocket and drone attacks by Hezbollah striking deeper and further away from the border.
Since early October, Israeli airstrikes in Lebanon have killed more than 450 people, mostly Hezbollah members, but also around 90 civilians and non-combatants. On the Israeli side, 21 soldiers and 13 civilians have been killed.
Ceasefire talks in Italy
Meanwhile, officials from the US, Egypt, Qatar and Israel are scheduled to meet in Italy on Sunday to discuss ongoing ceasefire negotiations.
CIA Director Bill Burns is expected to meet with Qatari Prime Minister Mohammed Bin Abdul Rahman al-Thani, Mossad director David Barnea and Egyptian spy chief Abbas Kamel, according to officials from the US and Egypt who spoke on condition of anonymity as they were not authorised to discuss the plans.
US officials on Friday said Israel and Hamas agree on the basic framework of the three-phase ceasefire deal pitched by US President Joe Biden.
Israeli Prime Minister Benjamin Netanyahu in his speech to the US Congress vowed to press ahead with the war until "total victory" over Hamas was achieved.
But those talks on Sunday may be complicated by an Israeli strike in Gaza on Saturday that killed at least 30 Palestinians sheltering in a girls’ school in Deir al-Balah.