The teenage son of an Israeli defence ministry contractor was killed Sunday on the Golan, in the most serious incident on the plateau since the Syrian war erupted in 2011.
Israel's defence ministry and the army said the 15-year-old was killed when a blast hit the car he was travelling in with his father and another contractor, both of whom were wounded.
The boy, an Arab Israeli, was Mohammed Qaraqra from the northern village of Arabeh in the Galilee region, military radio said.
The Israeli army called the explosion "an intentional attack" on a civilian vehicle by forces inside Syria, with a senior spokesman telling reporters Israeli tanks had fired at Syrian army posts in response.
It was not clear whether there were any casualties on the Syrian side.
"This is the most substantial incident on the border with Syria since the beginning of the civil war," said Lieutenant Colonel Peter Lerner, the army's foreign press spokesman, confirming it was the first death on the Israeli side.
He said the shooting was deliberate.
"This was an intentional attack, not errant fire," he said, adding that the target was a vehicle delivering water.
Military sources said the vehicle belonged to the defence ministry and was being used "as part of construction work on the border".
Israeli public radio cited security sources as saying that the Syrian army had fired the projectile, but the Israeli army declined to comment on the report.
- Blast source unclear -
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There was still some confusion over what caused the explosion, despite an earlier report by security sources who told AFP it was caused by a mortar round fired from Syria.
Lerner said the army was "not certain if it was an explosive device, a rocket or a mortar" that caused the explosion, noting there was a hole in the nearby fence.
"We responded with tank rounds at Syrian military posts in the immediate vicinity," he said, adding Israel would monitor events in the Golan and react "accordingly".
In March, Israeli warplanes attacked Syrian army positions just hours after a bomb wounded four Israeli soldiers on the Golan, one severely.
The bombing marked the most serious escalation along the ceasefire line with Syria since the 1973 Middle East War, with Israel's defence minister warning Damascus would pay a "high price" for helping militants bent on harming the Jewish state.
Over the past year, Israel has reportedly carried out a series of raids on Syrian and Hezbollah targets, but has not officially acknowledged doing so.
Lerner said it was unclear who was behind Sunday's incident.
"On the other side, we are aware of an extensive rebel, or opposition presence, but we can't confirm who was involved in it," he told reporters.
- Quneitra clashes -
The blast took place near Tel Khazeka, just south of Quneitra which is located in the centre of the plateau.
The Syrian Observatory for Human Rights said there was ongoing fighting in the area between Syrian military and rebels, adding regime forces had bombarded some villages in the Quneitra area.
An Israeli defence ministry official had earlier said the victim was a contractor.
Israel, which is still technically at war with Syria, seized 1,200 square kilometres (460 square miles) of the Golan Heights during the 1967 Six-Day War and later annexed it in a move never recognised by the international community.
Since the Syrian conflict erupted in 2011, the plateau has been tense, with a growing number of projectiles, mostly stray, hitting the Israeli side, prompting occasional armed responses.