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.
In Qatar on Sunday, fractious Syrian opposition groups finally struck a deal to form a new political and military coalition after a week of heated negotiations that nearly derailed on several occasions.
The new body, called the National Coalition for Revolutionary Forces and the Syrian Opposition, is intended to act as the single entity that manages the political and military affairs of the opposition. The action opens the way for more international humanitarian and military aid.
‘‘Today in Doha is the first time the different factions of the Syrian opposition are united in one body,’’ said Riad Hijab, a former Syrian prime minister and the highest-level defector from Bashir Assad’s government. ‘‘So we ask the international community to recognize the Syrian opposition as the representative of the Syrians.’’
The Israeli Army said that after the Syrian mortar round landed in the Golan on Sunday, causing no casualties or damage, troops fired ‘‘warning shots towards Syrian areas.’’
The army statement gave no details on the munitions used, but military officials later said a long-range antitank 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, Brigadier General Yoav Mordechai, as saying that the Israeli action 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.’’
The army said it had a filed a complaint through United Nations 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. Last week, a mortar shell landed outside an Israeli settlement without exploding.
Several days earlier, Israel complained to the UN that three Syrian tanks had entered a demilitarized zone, and last Monday the army said a stray bullet hit an Israeli army jeep.
Shlomo Brom, a retired general and senior research fellow at Tel Aviv University, said Sunday’s incident was unlikely to cause further escalation, if only because the embattled Syrian regime was not eager to open another front with Israel. Still, Brom said, he was concerned that with an Israeli election approaching in January, Israeli leaders may want ‘‘to be perceived by their constituency as tough.’’
One of the most contentious issues in the unification discussions in Qatar was the role of the Syrian National Council, the opposition group formed in August 2011. The council has been viewed by its foreign backers in recent months as ineffectual and out of touch with events on the ground in Syria.
Some members of the council pushed back hard against the US-backed initiative to form the new coalition, fearing it would mean the dissolution of their group. But many of the holdouts stood down under strong pressure from their colleagues who backed the initiative and from the opposition’s foreign supporters.
The council was offered additional seats to win its support and it will receive roughly one-third of the 60 seats in the new coalition.
Approximately one quarter of the seats also will be set aside for members from inside Syria, which will include a representative from each of the country’s 14 provinces.
‘‘The most important components are those coming from inside Syria, and they’re fully on board,’’ said Yaser Tabbara, a founding member of the council who helped shape the initiative to form the new coalition. Provisions also have been made to include minorities, and a handful of seats have been set aside for Kurdish and Alawite representatives.
The coalition will function as a sort of parliament rather than a government, according to participants in the discussions, and will be responsible for the creation of a legal committee, a military council, and a temporary government.
Supporters are pushing for quick recognition from the international community, to receive frozen Syrian government funds, take over Syrian embassies, and even pursue the seat of the Syrian government at the Arab League.
But it is the formation of the military council, which will include representatives from the Free Syrian Army as well as local militias and defectors, that may be the most important step.
The distribution of military aid to armed groups in Syria has been chaotic and led to in-fighting. Now, the countries giving military aid, which include Qatar and Saudi Arabia, can channel the weapons through a centralized body that could establish some degree of control over the process.