At least 11 people have been killed after a rocket attack struck a football field in the Israeli-controlled Golan Heights, wounding several others, according to Israeli authorities.
Most of the casualties are thought to be children and teenagers.
The assault came hours after an Israeli airstrike on south Lebanon killed three members of the militant Hezbollah group.
The attack is the deadliest on an Israeli target since war broke out in the region in October, when Hamas attacked Israel, killing some 1,200 people and taking 250 others hostage.
While the Israel Defence Forces (IDF) claimed Hezbollah was responsible for the airstrike, Mohamad Afif, head of Hezbollah’s media office, said the accusation was “false”.
Hezbollah said it struck a military base in the Golan Heights in retaliation for Israeli attacks on a village in Lebanon.
Israeli Prime Minister Benjamin Netanyahu warned that Hezbollah “will pay a heavy price for this attack, one that it has not paid so far,” his office said.
Mr Netanyahu, who was on a visit to the United States, said he would cut short his trip by several hours and would convene his security Cabinet after arriving.
The IDF said in a statement: “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.”
Israel’s Magen David Adom (MDA) paramedic service initially reported 11 people wounded, nine critically, all between the ages of 10 and 20.
Israeli Public Broadcaster Kan aired footage of some being rushed to ambulances on stretchers from a football field in the town of Majdal Shams.
“These were kids at a soccer field,” Beni Ben Muvchar, head of the local council, told Israeli broadcaster Channel 12.
“Today a red line was crossed,” he said, urging Israeli leaders to start targeting top Hezbollah commanders.
The Israeli military said one projectile was identified crossing from Lebanon toward the area, adding it was co-operating with the MDA to evacuate the wounded.
Channel 12 aired footage of a large blast in one of the town’s valleys.
Israel captured the Golan Heights from Syria during the 1967 Six-Day War and annexed them in 1981.
Hezbollah stated that its militants firing Katyusha rockets at an Israeli army post in the Golan Heights was in response to Israeli airstrikes on villages in south Lebanon.
The group said earlier that three of its members were killed on Saturday without specifying where.
Israel’s military said its air force targeted a Hezbollah arms depot in the border village of Kfar Kila, adding that militants were inside at the time.
The IDF and Hezbollah, an Iran-backed group based in Lebanon, have been exchanging cross-border fire since October. Hezbollah says it will halt its attacks on Israel once that country reaches a ceasefire deal with Hamas.
In response to Hamas’s attack in October, Israel launched an offensive in the Gaza Strip that has so far killed more than 39,000 people, according to local health authorities, displaced more than 80 per cent of the territory’s people and triggered a humanitarian disaster.
Over the past few weeks, the exchange of fire along the Lebanon-Israel has 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.
Additional reporting by PA news media
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