DOHA: The Syrian opposition struck a hard-won deal on Sunday on a new structure to take forward the 20-month uprising as clashes on the Golan Heights prompted what Israel said was its first fire across the armistice line since the 1973 Middle East war.

Participants in marathon talks in Qatar said discussions were continuing on details of a planned new government-in-waiting, but that the Syrian National Council had now heeded Arab and Western calls to join a new, wider coalition.

The Israeli warning shot across the UN-monitored ceasefire line between Syria and the occupied Golan Heights came after a mortar round fired from the Syrian side hit an Israeli position and after Prime Minister Benjamin Netanyahu told his cabinet Israel was “ready for any development.”

Reservations in SNC ranks about what many members saw as a move to sideline it had prompted repeated delays in the Doha talks and mounting frustration among other dissident groups and the opposition's Arab and Western supporters.

But after negotiations that ran into the early hours of Sunday and resumed in the afternoon, opposition officials said a deal had finally been done.

“We signed a 12-point agreement to establish a coalition,” said leading dissident Riad Seif, who drew up the US-backed reform proposals on which Sunday's agreement was based.

Another prominent opposition figure, Haitham al-Maleh, said a formal signing ceremony would held at 1700 GMT.

The deal came after the Syrian National Council, which had formerly been seen as the main representative of the opposition, heeded Arab and Western pressure to agree to a new structure embracing groups that had been unwilling to join its ranks.

Former prime minister Riad Hijab, who fled to neighbouring Jordan in August in the highest-ranking defection from President Bashar al-Assad's government, hailed the agreement as “an advanced step towards toppling the regime.”

Details of the deal have yet to be released, but Maleh said it was “no different” to the original proposals put forward by Seif, one of the leaders of the so-called Damascus Spring protest movement of a decade ago and now touted in Washington as a potential new opposition chief.

Seif's proposals envisaged the formation of a transitional government, a military council to oversee rebel groups on the ground and a judiciary to operate in rebel-held areas.

Mounting diplomatic pressure

There had been mounting diplomatic pressure on the opposition to overhaul its structures amid US-led accusations that the SNC had lost touch with civilian activists and rebels inside Syria and become little more than a talking shop for exiles.

International concern had been further raised by fears of a spillover of the conflict as fighting raged on Syria's borders with Iraq and Turkey as well as on the armistice line with the Israeli-occupied Golan.

The Israeli army said that a mortar round fired from the Syrian side had hit one of its positions on the Golan, prompting the riposte from its troops.

“A short while ago, a mortar shell hit an IDF (Israel Defence Forces) post in the Golan Heights adjacent to the Israel-Syria border, as part of the internal conflict inside Syria,” the army said in a statement.

“In response, IDF soldiers fired warning shots towards Syrian areas,” it added.

Military sources told AFP that the army fired a single Tamuz anti-tank missile, a weapon known for being highly accurate, towards the Syrian outpost from which the mortar round was fired.

“We shot toward them, but deliberately missed,” the sources said.

Chief military spokesman Yoav Mordechai said on his Facebook page that it was Israel's first firing across the armistice line since the 1973 war.

Earlier, Netanyahu said Israel was “closely monitoring what is happening on our border with Syria and there too we are ready for any development.”

Since Israel and Syria signed a 1974 disengagement agreement, a 1,200-strong unarmed UN force has patrolled a buffer zone on the Golan.

Fighting also flared on the Turkish border as Syrian troops and rebels battled for the town of Ras al-Ain, where thousands of refugees have fled into Turkey in recent days, the Syrian Observatory for Human Rights said.

Ras al-Ain is one of just two Turkish border crossings still controlled by the Syrian army. Rebels fighting to bring down Assad have captured four others while a seventh is controlled by Kurdish militia.

On Saturday, 121 people were killed in violence, the Observatory said, among more than 37,000 who have lost their lives since the uprising against Assad's rule erupted in March last year.