Last month al-Nusra launched two of its most ambitious operations to date. On December 10, the group occupied parts of a military base near Aleppo and two days later claimed responsibility for a coordinated suicide and car bomb attack on the heavily guarded Interior Ministry in the capital.
Al-Nusra's signature tactic, like that of AQI, is using large car and truck bombs driven by suicide bombers. The group has launched several such attacks against security installations in Damascus and Aleppo, sometimes as part of a coordinated assault involving gunmen.
Benotman says that last Summer al-Nusra launched a recruitment drive for suicide bombers and began stockpiling trucks and explosives. He says that weapons shortages among rebel groups means that al-Nusra's campaign of suicide bombings has allowed it to punch above its weight.
Last week al-Nusra demonstrated the lethality of a new tactic -- driverless car bombs operated by remote control, Benotman told CNN. He says the technology was used to destroy a gate at an airbase in Idlib and will raise fears that it could one day be used in an attack in the West.
If al-Nusra's fighting strength is some 5,000 members, as the Quilliam report estimates, that would be comparable to U.S. government estimates of AQI at the peak of the Iraq insurgency. But rebel commanders say that the group makes up less than 10% of the brigades fighting the regime.
While al-Nusra is mainly made up of Syrians, it includes a significant number of fighters from other Arab countries. In recent months a growing number have arrived from Saudi Arabia and the Gulf, but Iraqis and Jordanians constitute the majority of foreign fighters.
Cooperation with other rebels
In recent months, videos featuring rebels fighting in Syria have increasingly featured joint-operations between al-Nusra and other rebel groups.
According to the Quilliam Foundation report, al-Nusra often cooperates with other jihadist and Islamist groups such as Sukour al-Sham, which has several thousand fighters, and even with the Free Syrian Army, in a number of strategic battles, though joint operations between these two groups have not been widespread.
According to Benotman, a significant number of Jihadists fighting with other rebel outfits are wary of al Qaeda's hard-line ideology, but al-Nusra has sought to allay concerns by keeping its brand separate from al Qaeda, avoiding targeting civilians, and refraining from spelling out its true agenda.
"Preserving good relations with the other groups and treating them well and turning a blind eye to their mistakes is the foundation in dealing with the other groups, as long as they don't change," al-Nusra leader Mohammed al-Jawlani said in a December audio tape, according to a translation by the SITE Intelligence Group.
Al-Nusra and nine other local Jihadist brigades announced last month they were forming a regional unified command structure called the Mujahideen Shura Council in Deir el-Zour.
Yet according to Benotman's report, al-Nusra has not yet formed any such coalitions with larger Islamist rebel outfits such as Ansar al-Islam, Ahrar al-Sham, and the Deir Ezzor Revolutionary Council, three groups which previously joined together to form the "Liberation Front."
A counterproductive designation?
According to the Quilliam study, "the designation (by the U.S.) of al-Nusra as a terrorist organization has only served to reinforce jihadist support for the group.
Nada Bakos, the former CIA agent agreed, telling CNN the designation may elevate al-Nusra's status amongst Jihadists worldwide, increasing funding and recruitment for the group.
Benotman's study describes relations between al-Nusra and the FSA as mixed, with both realizing they need each other in the short term to topple al-Assad.
"Some FSA brigades threaten to work with al-Nusra if the West does not provide enough weapons while others see al-Nusra as trying to exploit the revolution for their own ends, instead of working for the good of the country. Jabhat al-Nusra and the Free Syrian Army are wary of one another, as they are already vying for popularity amongst the population," Quilliam says.
Bakos, the former CIA official says AQI and al-Nusra are likely replicating the flexible, decentralized, and resilient external operations networks established by al-Zarqawi in the region, and that makes them a force to be reckoned with. Benotman says the al-Zarqawi networks never really went away.
Analysts believe al-Nusra's hostility to the West could create an "over-the-horizon" threat to the United States and its allies if the group is able to secure a foothold in Syria and across the Levant.
In such a scenario al Qaeda aligned groups would be operating within touching distance of borders of Israel, improving their potential to launch a direct attack against the country, long a key proclaimed objective of the terrorist network's leader Ayman al-Zawahiri.
The Quilliam Foundation report is sobering reading at a time when increasing sectarian tension and regime brutality in Syria are playing into al-Nusra's hands.
Benotman believes al-Nusra doesn't want a quick end to the al-Assad regime.
"The longer the conflict goes on, the stronger they will get," he told CNN.