DOHA: Syria’s deeply divided opposition has agreed to unite against President Bashar al-Assad, electing a moderate cleric as leader in a move hailed by the West as a step towards a peaceful political transition.

After four days of marathon talks in Qatar, the Syrian National Council (SNC) finally signed up to a wider, more representative bloc centered on a government-in-waiting, as demanded by Arab and Western states.

The breakthrough came amid Western concerns the Syrian conflict is increasingly spilling over its borders, after Israel fired a warning shot across the UN-monitored ceasefire line between Syria and the occupied Golan Heights.

Muslim cleric Ahmed Moaz al-Khatib, 52, a Damascus moderate who quit Syria three months ago, was elected head of the new grouping, with prominent dissident Riad Seif and female opposition figure Suhair al-Atassi chosen as his deputies.

The United States swiftly declared its support for the new National Coalition.

“We look forward to supporting the National Coalition as it charts a course toward the end of Assad’s bloody rule and the start of the peaceful, just, democratic future that all the people of Syria deserve,” State Department deputy spokesman Mark Toner said in a statement.

Britain and France also hailed the Doha agreement.

The Israeli warning shot came after a mortar round from the Syrian side hit an Israeli position.

It followed comments by Prime Minister Benjamin Netanyahu that Israel was “ready for any development” and as his defense minister warned a “tougher response” would follow.

United Nations (UN) leader Ban Ki-moon appealed to Israel and Syria to ease tensions on their disputed Golan frontier.

Syrian new opposition leader Khatib urged the international community to “fulfil its pledges”.

“Our people are subjected to a systematic genocide,” he said at the signing ceremony in Doha.

The newly elected head of the SNC George Sabra said that Syrian rebels need weapons “not just bread and water.”

Qatari Prime Minister Sheikh Hamad bin Hassem Al-Thani said that he would accompany Khatib on Monday to the Arab League’s headquarters in Cairo.

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 ran into the early hours of Sunday and resumed in the afternoon, the anti-Assad factions agreed to form a “National Coalition of Forces of the Syrian Revolution and Opposition.”

“We signed a 12-point agreement to establish a coalition,” said Seif, who championed the US-backed reform proposals on which the agreement was based.

In a copy of the document obtained by Agence France-Presse, the parties “agree to work for the fall of the regime and of all its symbols and pillars,” and rule out any dialogue with Assad’s government.

They agreed to unify the fighting forces under a supreme military council and to set up a national judicial commission for rebel-held areas.

A provisional government would be formed after the coalition gains international recognition, and a transitional government after the regime has fallen.