Bashar al-Assad.

A new jihadist group with links to al-Qaeda is emerging as one of the most power groups within the Syrian rebellion and may have as many as 5,000 terrorists in Syria, according to a new study.

The group—called Jabhat al-Nusra—was designated as an al-Qaeda affiliate by the U.S. government last month and “has shown itself to be the principal force against Assad and the Shabiha [armed government gangs and militias],” according to a study by the London-based Quilliam Foundation obtained by CNN.

“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.

According to a report put out by the U.S. State Department in December 2012, al-Nusra is an offshoot of al-Qaeda in Iraq (AQI), a group founded by slain terrorist leader Abu Musab al-Zarqawi.

“Al-Nusra has sought to portray itself as part of the legitimate Syrian opposition while it is, in fact, an attempt by AQI to hijack the struggles of the Syrian people for its own malign purpose,” the State Department statement read.

The confirmation of al-Qaeda affiliated groups within the rebellion against Syrian President Bashar al-Assad is likely to stir further anxiety in the West. The U.S. and other Western allies have been reluctant to provide support to the rebellion out of fears of empowering jihadists.

At a cabinet meeting on Jan. 6, Israeli Prime Minister Benjamin Netanyahu also mentioned “global jihadist forces” within the Syrian rebellion and announced plans to erect a security fence along the Israeli-Syrian border in the Golan Heights.