(Adds more Israeli strikes, Netanyahu comment, details; in paragraphs 2, 5-6)
JERUSALEM, June 22 (Reuters) - An attack from inside Syria on Sunday killed a 13-year-old Israeli boy on 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. Israel launched more strikes later from the air and land at nine Syrian army positions, including a military headquarters, the army said. It confirmed direct hits on the targets.
The Defence 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.
Prime Minister Benjamin Netanyahu accused the attackers of indiscriminate killing of Israeli citizens.
"The enemies of the state of Israel use all means, they don't hesitate to attack civilians and kill children ... they do not differentiate between Israel's Jewish and non-Jewish citizens," he said.
A military spokeswoman said an anti-tank missile fired from Syria across the frontier fence on the Golan had struck the water tanker in which Qaraqara had been travelling.
"This is the most substantial event that we have had on the border with Syria since the beginning of the (Syrian civil) war," a military 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 western part of the plateau from Syria in a 1967 war and annexed it in a move that is not internationally recognised.
While the Syrian army has a presence on the Golan, some areas are controlled by rebels fighting to topple President Bashar al-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. (Reporting by Ari Rabinovitch, Dan Williams, Allyn Fisher-Ilan and Ori Lewis, Editing by Jeffrey Heller, Rosalind Russell and Mohammad Zargham)