* Clash highlights divisions in the opposition
* Ceasefire deal posted on rebel group's Facebook page
BEIRUT, Sept 20 (Reuters) - Al Qaeda-linked fighters and a rival Syrian rebel group declared a truce on Friday after two days of clashes near the Turkish frontier in which the militant Islamists overran a border town, rebels said.
Fighters from an al Qaeda affiliate, the Islamic State of Iraq and the Levant (ISIL), on Wednesday killed at least five members of the Northern Storm Brigade, a rebel group that controls the border.
Clashes continued on Thursday, highlighting deep divisions in the opposition that is fighting to overthrow President Bashar al-Assad in Syria's 2-1/2-year-old civil war.
The fight in the town of Azaz was one of the most serious between ideologically moderate rebels and ISIL, which is made up largely of foreign fighters. It prompted Turkey to shut a border crossing.
A ceasefire agreement posted on the Northern Storm Brigade's Facebook page was signed by both parties and negotiated by the powerful Islamist Tawheed Brigade, which is based in Aleppo, about 20 miles (30 km) south of Azaz.
The pact called for an immediate ceasefire, the release of prisoners and for a dispute over control of the border post with Turkey to be referred to a rebel court. (Reporting by Oliver Holmes; Editing by Mark Trevelyan)
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