Tel Aviv, Israel - A rocket fired from Lebanon hit a soccer field in an Arab town in the Israeli-annexed Golan Heights Saturday, killing 11 youngsters in what the army described as the "deadliest attack on Israeli civilians since October 7."

The army said Lebanese militant group Hezbollah fired the deadly rocket that killed the youngsters aged between 10 and 20 years when they were hit on the field in the town of Majdal Shams.

Many residents of the town retain Syrian nationality decades after the territory's occupation in the 1967 Arab-Israeli war.

The rocket fire came after an Israeli strike killed four Hezbollah fighters in south Lebanon, prompting the Iran-backed militant group to announce a flurry of retaliatory rocket attacks against the Golan and northern Israel.

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Military spokesman Daniel Hagari said on X that 11 youngsters were killed in the attack, while the emergency service Magen David Adom said 19 others were wounded when the rocket hit Majdal Shams.

"We will prepare for a response against Hezbollah... we will act," Rear Admiral Hagari said in a video statement, adding the rocket fire was the "deadliest attack on Israeli civilians since October 7" when Hamas militants attacked southern Israel, sparking the war in Gaza.

Prime Minister Benjamin Netanyahu, who was returning early from a visit to the US, vowed that "Israel will not let this murderous attack go unanswered."

"Hezbollah will pay a heavy price for it, a price it has not paid before," he warned in a statement released by his office.

Israeli President Isaac Herzog charged that Hezbollah had "brutally attacked and murdered children today, whose only crime was going out to play soccer."

Hezbollah denied it was responsible for the deadly strike.

"The Islamic Resistance has no connection to this incident," it said, referring to its military wing.

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The police and the army said the rocket fired at Majdal Shams was part of a barrage of rockets fired from Lebanon, which struck multiple locations in the Golan.

Ambulances, helicopters, and mobile intensive care units were deployed to the scene, the army said.

"We arrived at a football pitch and saw destruction and objects on fire. Injured people were lying on the grass," paramedic Idan Avshalom said in a statement issued by Magen David Adom.

An AFP correspondent saw medics carrying away the wounded for treatment.

"Officers and police bomb disposal experts from the northern district police are currently securing the area and searching for additional [rocket] remnants to eliminate any further risk to the public," the police said in a separate statement.

The rocket fire came after a Lebanese security source said an Israeli strike killed four Hezbollah fighters in the southern village of Kfar Kila.

Hezbollah, which has exchanged near-daily cross-border fire with the Israeli army since the Gaza war erupted last October, confirmed the deaths of four of its fighters.

It said it carried out a dozen retaliatory attacks on Israeli targets, nine in the space of two hours.

The violence since October has killed at least 527 people in Lebanon, according to an AFP tally. Most of the dead have been fighters, but they have included at least 104 civilians.

On the Israeli side, 18 soldiers and 24 civilians have been killed, according to Israeli authorities.