JERUSALEM — Israel fired a missile into Syria in what the military described as a “warning shot,” after a stray mortar shell fired from Syria landed near an Israeli military post in the Golan Heights. It was the first time Israel fired into Syria since the civil war erupted there more than a year and a half ago.

Fighting between Syrian government forces and rebels has been moving closer to Israeli-controlled areas of the Golan, which Israel captured from Syria during the Middle East war of 1967.

Israel says it is not being deliberately targeted by Syrian forces. But at the weekly Cabinet meeting in Jerusalem, Prime Minister Benjamin Netanyahu warned that Israel will not allow the Syrian civil war to spill across the northern boundary.

Netanyahu said Israel is closely watching the situation and is prepared for any eventuality.

Violence has also surged on Israel’s southern border with the Gaza Strip, which is ruled by the Palestinian militant group Hamas. Palestinian militants bombarded southern Israel with rockets, sending families to bomb shelters and shutting schools. Israel retaliated with airstrikes which the army said targeted weapons facilities.

The violence began Saturday when a Palestinian anti-tank missile blasted an Israeli army jeep on the Gaza border.

Prime Minister Netanyahu said Palestinian attacks from Gaza will not be tolerated.

Netanyahu said “Israel will not sit idly by” when its citizens are attacked, and he warned that the army is prepared “to escalate its response.”

Hamas was defiant. The group’s spokesman, Fawzi Barhoum, said the Palestinians would “teach Israel a lesson.”

Barhoum told Hamas television that Israel is “shooting at Gaza day and night and killing women and children.” He said “resistance is our right.”

Despite the warnings, both sides have signaled that they do not want an escalation like the one that sparked Israel’s invasion of Gaza nearly four years ago and caused massive destruction. But with tit-for tat attacks across the border, neither side is backing down.