Israel carried out airstrikes on nine Syrian army positions early Monday in response to a cross-border attack on the Golan Heights plateau in Israel’s north that killed an Israeli teenager and injured two Israeli civilians.

The attack by Israeli forces killed at least 10 people, making the strike the gravest escalation of ceasefire breaches between the two countries since the 1973 Middle East War, Agence France-Presse, or AFP, reported. Sunday's blast killed an Israeli teenager who was traveling along with another person in a defense ministry car driven by his father on the Syria-Israel border, both of whom were injured in the explosion.

"Today's event on the Syria border intentionally targeted Israelis. The explosion is the most serious attack against Israel in recent months," Israel Defense Forces, or IDF, tweeted from its account Sunday, while IDF’s spokesperson Lt. Col. Peter Lerner said: "This is not a case of errant fire, but of an intentional attack."

The army spokesperson had said that Israeli army tanks fired on Syrian army posts shortly after the blast occurred on Sunday. Nearly 196 square miles of the Golan plateau, which was seized by Israel in 1967, is still under Syria’s control and, since the anti-government protests escalated in 2011 in Syria, the region has seen constant tension.

“Israel's enemies will stop at nothing,” Israeli Prime Minister Benjamin Netanyahu said, according to AFP, condemning the act, adding: “They won't stop at attacking civilians or even murdering children as happened this morning.”

Lerner said, according to AFP: “Yesterday's attack was an unprovoked act of aggression against Israel... The IDF will not tolerate any attempt to breach Israel's sovereignty and will act in order to safeguard the civilians of the State of Israel,” adding: “This is the most substantial incident on the border with Syria since the beginning of the civil war."

The attack follows an attack in March where Israeli warplanes attacked Syrian army positions a few hours after a bomb exploded in Golan Heights, wounding four Israeli soldiers.