A new generation of al Qaeda militants coming of age in Syria is transforming the group into an organization with a mass base of support, a senior commander in the group exclusively told VICE News.

The high-ranking leader in al Nusra Front, al Qaeda's Syrian affiliate, asked to be known as Sheikh Abdu Salam. He spoke unmasked for the first time in an unprecedented interview, where he talked about his life and the future of the group.

"They fought the regime with other brigades, they lived among the people, they went up to the pulpits and gave the Friday sermon, they gave lessons and lectures, they have media activities, they fought in the frontline and gave martyrs and leaders," Abdu Salam said of al Nusra's members.

The commander spoke to VICE News for a forthcoming documentary, Inside the Battle: Al Nusra-Al Qaeda in Syria, made while spending over a month with the group.

Abdu Salam, who claims to have been imprisoned and tortured by President Bashar al-Assad's regime before he joined al Nusra, said that the outbreak of revolution in Syria during 2011 inaugurated a new phase in the group's evolution, allowing it to build social service organizations and demonstrate its ideas for the first time.

Like its bitter rivals Islamic State (IS) — from which it split in 2013 — al Nusra's willingness to use suicide bombing and other self-sacrificial tactics has bolstered the group's strength on the battlefield.

Abdu Salam repeatedly referred to IS as the khawarij, a reference to a warlike sect in early Islam who rebelled against mainstream religious authority.

"They assault Muslims, and their ideology completely drifted from the Sunni ideology that we follow, so we have to fight them," he said. "Is it also due to the frequent assaults on the Syrian people."

Al Nusra itself has frequently been accused of brutality. When it overran the Abu Al-Duhur airbase in September, it reportedly executed 56 captive Syrian soldiers. Human Rights Watch has accused the group of "systematic and widespread violations including targeting civilians, kidnappings, and executions."

It is not known how many thousands of fighters al Nusra can now count on, but it is widely acknowledged to be rivaled for size and strength in northwest Syria only by the more moderate Ahrar al Sham, with which it is allied in the Jaysh al Fatah (Army of Conquest) coalition with several other groups.

"The media makes a lot of noise about changes in people's support to al Nusra: this is not true," Abdu Salam said. "There are still many people coming to join al Nusra Front, the numbers of our camps and people are increasing. The areas they operate in are also growing."

After scoring a series of victories over US-backed rebels in northwest Syria over the summer, al Nusra is now under pressure from a renewed government offensive backed by Russian airstrikes.

Abdu Salam, speaking before the recent regime offensive begun, argued that it was the group's strategy of developing social services and popular support that was key to their success, as well as to the evolution of al Qaeda as an organization.

'Al Nusra Front is the group that cares most about providing everyday needs to Muslims in Syria'

"The difference between al Qaeda's first generation and the second is that the first one worked in secret, in areas under the control of tyrants, like Syria and other countries, " he said. "There wasn't a revolution, or areas liberated from these regimes where we could have big training camps, recruit big numbers and explain to people the methods we believe in, and spread these ideas among Muslims, to get their attention."

"Of course that stage was a preparation for this stage," he continued. "That stage was preparing intellectual and military elites."

That preparation was particularly difficult, Abdu Salam said, in countries like Syria where al Qaeda was not able to have a public presence.

"The numbers were few, there were major security difficulties, none of us could move freely, or read the books we wanted to, or even sit with people and explain to them the ideas we believe in," he added.

That has now changed. Alongside al Qaeda in the Arabian Peninsular in Yemen and al Shabab in Somalia, al Nusra is part of a generation of the organization that can defend territory, albeit as insurgents rather than stable states. Yet, it also administers rudimentary social services to the areas under its control.

That's why the group is popular, claimed Salam, alluding to demonstrations when it was listed as a terrorist organization and bombed by the American-led international coalition.

"Al Nusra Front is the group that cares most about providing everyday needs to Muslims in Syria through well-known services and establishments, such as municipal services, administration, mills, and bakeries," he said.

"[We run] judicial institutions that focus on resolving conflicts and disputes so people's daily lives can continue," he added. "By getting rid of corrupt people in many areas of Syria, people support and empathize with al Nusra."