* YouTube video shows over 40 fighters
* Russia has estimated around 200 citizens fighting in Syria
* Moscow a major backer of Syria's Assad
BEIRUT, Sept 4 (Reuters) - A group of Islamist militants from Russia's volatile North Caucasus region fighting in Syria have split with a major al Qaeda-linked rebel unit to form an independent battalion, according to a video posted online.
Militants who have travelled from Russia's North Caucasus region, where the Kremlin is fighting an Islamist insurgency, have emerged as some of the most effective fighters waging battle against President Bashar al-Assad.
A group calling itself "Mujahideen of the Caucasus in the Levant" announced its decision to split from the Islamic State of Iraq and the Levant (ISIL) in a video posted on YouTube on Sept. 3. The video's authenticity could not be immediately verified.
"We are leaving the Islamic State in Iraq and the Levant, and our battalion is independent," a bearded fighter wearing camouflage fatigues said in Russian, as another fighter translated into Arabic.
The video showed over 40 other fighters, many wearing face masks and equipped with assault rifles.
Russia has estimated that about 200 of its citizens are fighting alongside Syrian rebels.
Their presence puts in focus the security risks they may pose if they return to the Russian region, which borders the area where Moscow plans to host the Sochi 2014 Winter Olympics.
Moscow has repeatedly sought to protect Assad in the U.N. Security Council.
Rami Abdelrahman, head of the Britain-based Syrian Observatory for Human Rights monitoring group, said the split appeared to be rooted in the north Caucasus group's desire to distance itself from disputes between ISIL and other rebels.
Activists in northern Syria where the group is fighting also pointed to ideological and political differences among Islamist leaders as a possible source of the defection.
Divisions among rebel fighters - as well as the influence of hardline Islamists - is one reason Western powers have hesitated to intervene in Syria's two and a half year-old conflict, in which over 100,000 people have died. (Reporting by Alexander Dziadosz in Beirut and Thomas Grove in Moscow; Editing by Yara Bayoumy and Ralph Boulton)