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By Lisa Barrington and Suleiman Al-Khalidi

BEIRUT, July 28 (Reuters) - Al Qaeda told its Syrian branch, the Nusra Front, that it could break organisational ties with global jihadist organisation to preserve its unity and continue its battle in Syria, in an audio statement released on Thursday.

A break with al Qaeda could pave the way for greater support from Gulf states such as Qatar for Nusra Front, the most powerful faction in Syria's five-year conflict opposing both President Bashar al-Assad and the Islamic State militant group. It could also lead to closer ties between Nusra and other fighting factions in Syria.

"You can sacrifice without hesitation these organisational and party ties if they conflict with your unity and working as one body," al Qaeda leader Ayman al-Zawahri said in an audio statement directed to the Nusra Front.

"The brotherhood of Islam among us is stronger than any organisational affiliation ... Your unity and unification is more important to us than any organisational link."

Listed as a terrorist organisation by the United States, Nusra Front was excluded from Syria's February cessation of hostilities truce and Russia and the United States are also discussing closer coordination to target the group.

Speaking before Thursday's announcement, Charles Lister, an expert with the Middle East Institute, said that while Syria's opposition has always demanded Nusra leave al Qaeda, Western powers are unlikely to change their assessment of the group.

U.S. Secretary of State John Kerry has proposed closer cooperation with Russia against Nusra Front, including sharing intelligence to coordinate air strikes against its forces.

Aymenn Jawad Al-Tamimi, a research fellow at U.S. think tank Middle East Forum, said a formal break with al Qaeda and the possible formation of a new coalition of fighters with al Qaeda's blessing "arguably represents the worst outcome from the U.S. perspective".

He said it would make "targeting of terrorist figures much more difficult as they will be ever more deeply embedded in the wider insurgency".

A larger coalition between the Nusra Front and other groups "would then quickly and easily dismantle many of the U.S.-backed groups among the Syrian rebels in the north", he wrote.

Nusra Front was set up shortly after the uprising against Assad broke out in 2011. Originally supported by Islamic State, which controls swathes of territory in Syria and Iraq, it split from the hardline group in 2013.

It has been sanctioned by the U.N. Security Council, although in many parts of Syria it frequently fights on the same side as mainstream groups favoured by Washington and its Arab allies.

Rebels fighting under the banner of the Free Syrian Army have denied direct coordination with Nusra, which has also fought and crushed several Western-backed rebel groups.

After lying low in the early days of the February truce, Nusra has re-emerged on the battlefield as diplomacy has unravelled, spearheading recent attacks on pro-government Iranian militias near Aleppo, Nusra commanders and other rebels say.

Proposals to distance Nusra from al Qaeda have been floated before. Last year, sources told Reuters that the group's leaders considered cutting ties with al Qaeda to form a new entity backed by some Gulf Arab states seeking to topple Assad but which are also hostile to Islamic State.

(Additional reporting by John Davison and Dominic Evans in Beirut, Ahmed Tolba in Cairo; Editing by Catherine Evans) ((lisa.barrington@thomsonreuters.com; +961)(0)(1954456;))