JERUSALEM – Israeli forces in the Golan Heights fired into Syria on Sunday after a stray mortar round from fighting between Syrian troops and rebels hit an army post, the Israeli military said, calling the response a “warning.”

The incident was said to be the first time Israel had fired across the Golan frontier into Syria since the 1973 Middle East war, and it underlined concerns that Syria’s civil war could draw in neighboring countries and trigger wider conflict in the region.

Israel captured the Golan, a strategic plateau overlooking northern Israel, in the 1967 Six-Day War and annexed the area in 1981. The cease-fire line there has been quiet for decades, but Israeli officials have voiced concerns that the upheaval in Syria could spill over the frontier.

An Israeli army statement said that after the mortar round landed Sunday, causing no casualties or damage, troops fired “warning shots towards Syrian areas.” The statement gave no details on the munitions used, but military officials later said a long-range anti-tank missile had been fired in the vicinity of a Syrian mortar battery thought to have fired the shell.

Army Radio quoted the chief military spokesman, Brig. Gen. Yoav Mordechai, as saying that the Israeli fire was meant to send “a clear message to the Syrian army that Israel will not accept continued fire in its direction … even if it is not deliberate.”

Meanwhile, The Associated Press reported that Syrian anti-government groups struck a deal Sunday to form a new opposition leadership that will include representatives from the country’s factions fighting to topple President Bashar Assad’s regime.

Ali Sadr el-Din Bayanouni, a former Syrian Muslim Brotherhood leader, said the new leadership will be called the Syrian National Coalition for Opposition and Revolutionary Forces, the AP reported.