The upheaval in Syria drew a military response from Israel on Sunday when its forces fired a guided antitank missile near a Syrian mortar battery after a stray shell from fighting between Syrian troops and rebels hit an Israeli army post in the Golan Heights, military officials said.

The missile firing into Syria, which the army called a “warning,” signaled a more active Israeli posture toward the Syrian conflict after several recent incidents in which errant munitions have fallen in Israeli-held territory.

Israeli officials have watched with growing concern as the fighting in Syria has spread to areas near the Golan Heights, a strategic plateau captured in the 1967 Six-Day War and later annexed by Israel.

The cease-fire line there between Israeli and Syrian forces has been quiet for decades, but Israeli military officials have been preparing for the possibility that the turmoil in Syria could spill over the frontier.

Sunday’s incident was said to be the first time that Israel had fired across that line since the 1973 Middle East war, and it underscored fears that the violence in Syria could draw in neighboring countries and trigger wider conflict in the region. The fighting has led to skirmishes on the borders of Turkey, Jordan and Lebanon.

Israel fires at Syria after stray mortar strikes army post

On Sunday, after a mortar round from Syria hit an Israeli army outpost in the central Golan Heights, Israeli forces fired a Tamuz missile — a precision antitank weapon with a range of more than 10 miles — near a Syrian mortar battery thought to have fired the errant shell, military officials said.

Israeli Defense Minister Ehud Barak said that the firing was “a signal to the Syrians that we will not tolerate more firing into our territory,” and he warned that “additional firing into Israeli territory will provoke a harsher response and exact a price from Syria.”

The army said it had filed a complaint through U.N. forces stationed between Israeli and Syrian forces in the Golan, conveying a warning that continued fire from Syrian territory “will not be tolerated and shall be responded to with severity.”

There have been several incidents this month in which stray munitions from the fighting in Syria have reached the Israeli-held Golan Heights, causing no casualties or damage.

Itamar Rabinovich, a former Israeli ambassador to the United States who led negotiations with Syria in the 1990s, said that despite Sunday’s incident there were no indications that Israel was about to depart from its policy of staying out of the Syrian conflict.

“Israel has scrupulously avoided meddling in the Syrian crisis because it knows that it would be inflicting political damage on the opposition, and I don’t think this has changed,” he said. “At the same time, I think that the threshold for tolerating violence on yet another border is very low.”

Rabinovich was referring to a parallel flare-up in fighting across the border with the Gaza Strip that began Saturday.

“I don’t think the government wants to see another active front on the Golan Heights . . . so it probably decided to nip it in the bud,” he said.

Shlomo Brom, a retired general and senior research fellow at the Institute for National Security Studies at Tel Aviv University, said the Golan incident was unlikely to cause further escalation, if only because the embattled Syrian regime was not anxious to open another front with Israel. Still, Brom said, he was concerned that with an Israeli election approaching in January, political considerations might be influencing Israeli leaders who want “to be perceived by their constituency as tough.”

As tensions rose on the northern front Sunday, alerts sounded across southern Israel, sending residents running for shelter as fresh volleys of rockets and mortar shells were fired from the Gaza Strip, wounding four people. The fighting was triggered Saturday when an antitank missile fired from Gaza hit an Israeli border patrol jeep, wounding four soldiers. Israeli shelling in response killed four Palestinians and wounded about two dozen more.

A Palestinian militant was killed Saturday night in what the army said was an airborne strike on a rocket squad. The army said 75 mortar shells and rockets were fired at Israel on Sunday, including a longer-range Grad rocket intercepted by Israel’s Iron Dome missile defense system near the city of Beersheba.

Speaking at the weekly meeting of his cabinet, Israeli Prime Minister Benjamin Netanyahu said that the army would act “firmly against the terrorist organizations in the Gaza Strip,” adding: “We are prepared to intensify the response.”

Barak said Sunday that a ground assault could not be ruled out.

“If we are compelled to go back into Gaza to strike Hamas and restore security to the residents of Israel, we will not hesitate,” he said.