For the first time since the 1973 Yom Kippur War, Israeli forces on Sunday fired over the country’s northern border to Syria as a warning after a mortar shell fired from Syrian territory exploded in the Golan Heights, officials say.

The Israeli newspaper Ynet reported the Israeli Defense Forces Artillery Corps fired at a post in Syria in response. On Thursday, three Syrian mortar shells struck in and around an Israeli village in the Golan Heights.

The IDF vowed in a statement, “Further attacks [from Syria] will illicit a vigorous response,” the Jerusalem Post reported.

A longer statement posted on the IDF spokesman’s website read:

A short while ago, a mortar shell hit an IDF post in the Golan Heights adjacent to the Israel- Syria border, as part of the internal conflict inside Syria. No damage or injuries have been reported.

In response, IDF soldiers fired warning shots towards Syrian areas.

The IDF has filed a complaint through the UN forces operating in the area, stating that fire emanating from Syria into Israel will not be tolerated and shall be responded to with severity.

According to the Post, IDF officials believe the Syrian shell fell over the border unintentionally due to the ongoing fighting between the forces of President Bashar Assad and opposition forces trying to oust him.

The errant shell caused no injuries or damage to property.

IDF Spokesman Brig. Gen. Yoav Mordechai believes there were no casualties on the Syrian side from the warning shots.

The Jerusalem Post quoted an unnamed source who said, “This was a signal to the Syrians that we will not be so forgiving of everything that lands in a territory.”

Brig. Gen. Mordechai told the Times of Israel: “We have no interest in getting in between the rebels and the Syrian army, but to defend the Golan Heights from stray fire.”

Earlier on Sunday, Israeli Defense Minister Ehud Barak said in an interview with Army Radio that Israel would respond to further incidents of explosives hitting the Golan Heights, which is home to both Jewish and Druse Arab residents.

“The message has certainly been relayed. To tell you confidently that no shell will fall? I cannot. If a shell falls, we will respond,” Barack said.

The Jerusalem Post further reported:

At the Sunday cabinet meeting, Prime Minister Binyamin Netanyahu said that Israel was closely following events along the Syrian border, and was prepared for all possibilities on that front.

Israel told Syrian President Bashar Assad on Saturday to rein in attacks on rebels near the Golan, which had been mostly quiet for decades.

The Thursday mortar at Moshav Alonei Habashan was one of three Syrian mortar shells that struck the Golan that day, marking a significant deterioration of security conditions along the border.

All of this rasies concern that the Syria conflict could expand to neighboring countries, leading to a wider conflagration.

Israel captured the Golan Heights from Syria during the 1967 Six Day War. In 1981, Israel annexed the territory, placing it under Israeli law, but Syria has always insisted it wants the territory back.

This story has been updated to include new detail and quotes.