By Nic Robertson and Paul Cruickshank
A jihadist group with links to al Qaeda has become the most effective of the different factions fighting the regime, according to a new analysis, and now has some 5,000 fighters.
The group is Jabhat al-Nusra, which was designated an al Qaeda affiliate by the United States government last month. It is led by veterans of the Iraqi insurgency "and has shown itself to be the principal force against Assad and the Shabiha," according to the study.
CNN obtained an advance copy of the analysis, set to be released Tuesday by the Quilliam Foundation, a counterterrorism policy institute based in London.
"The civil war in Syria is a gift from the sky for al-Nusra; they are coasting off its energy," the lead author of the report, Noman Benotman, told CNN.
Benotman, a former prominent Libyan Jihadist who was personally acquainted with al Qaeda's top leaders including Osama bin Laden and Ayman al-Zawahiri, consulted Western and regional intelligence officials as well as jihadists in Syria, including "al-Nusra sources."
And at a time of optimism that the global threat from al Qaeda terrorism has crested, the study will fuel anxiety in Western capitals that a powerful al Qaeda affiliate may become entrenched in the heart of the Arab world, creating deep challenges in any post- al-Assad Syria, and a new threat to international security.