JERUSALEM — An attack from inside Syria on Sunday killed a 13-year-old Israeli boy in the occupied Golan Heights, the first fatality on Israel's side of the frontier since the Syrian civil war began, relatives and the military said.

Israeli tanks fired at Syrian army positions in response to what an Israeli military spokesman described as an intentional attack.

The Defense Ministry said the teenager, an Arab citizen of Israel from a village in the Galilee, had accompanied his father, one of the ministry's civilian contractors, to the Golan, and that two other people were wounded in the incident.

Israeli officials initially said the boy, Mohammed Qaraqara, was 15. Relatives said he was 13. "He was an excellent student, everyone loved him," his cousin, Salah Qaraqara, 52, told Reuters.

A military spokesman said it was not yet clear whether a roadside bomb or an artillery shell or mortar round, fired from Syria across the frontier fence on the Golan, had struck the water tanker in which the group had been traveling.

"This is the most substantial event that we have had on the border with Syria since the beginning of the (Syrian civil) war," the spokesman said.

Shelling from the Syrian civil war has occasionally spilled over onto the Golan, including what Israel has said were deliberate attacks on its troops. Israel captured the plateau from Syria in a 1967 war and annexed it in a move that is not internationally recognized.

While the Syrian army has a presence on the Golan, some areas are controlled by rebels fighting to topple President Bashar Assad, including al Qaeda-inspired militants hostile to the Jewish state.

Israel says Hezbollah guerrillas from Lebanon are also operating, on Assad's behalf, on the Golan. Israeli officials have voiced concern that Israel will increasingly become a target during and after the Syrian conflict.

Last March, four Israeli soldiers were wounded in a roadside bombing along the Golan frontier. Israel responded to that incident by launching air strikes against Syrian military sites.