France's super jihadi and the teenage girl trapped in Syria

Omar Omsen looks like a regular office worker. Only the camouflage t-shirt and the tent walls billowing around him offer a hint that this is no ordinary workplace, but the epicenter of jihadi recruitment in Syria.

The clip he's working on is not a pop video or newsreel but a piece of radical Islamist propaganda, in praise of the "Charlie Hebdo" attackers who killed 12 people in Paris in January 2015.

Omsen, a.k.a. Omar Diaby is France's "super jihadist."

r Omsen leads a French "katiba," or battalion, in Syria. He was radicalized while in prison.

Through his series of online videos, released under the name "19HH" (a tribute to the 19 perpetrators of the September 11 attacks), French authorities say he is responsible for recruiting about 80% of French-speaking jihadis heading to Syria and Iraq.

The clips fuse Hollywood special effects, rap music, religion and conspiracy theories in an attempt to convince young French Muslims to join the fight.

Omsen, 41, was born in Senegal, but moved to France as a child, and grew up in Nice. According to French media reports, he became radicalized during several spells in prison. He moved to Syria in 2013, to head up a French "katiba," or brigade, of jihadis.

Among his followers, who listen rapt as he preaches with messianic fervor, Omsen is treated as a spiritual leader.

All the guys were looking at him like he was god, like it was a sect," says Fouad El Bathy, who has seen Omsen in action up close in Syria.

"He made me think of a guru -- they were venerating him."

El Bathy was in Syria to try and rescue his baby sister, Nora, who ran away to Syria when she was just 15 years old, one of the thousands who have made the journey.

Hotbed of recruitment

The Institute for Economics and Peace says between 25,000 and 30,000 foreign fighters, 21% of them from Europe, traveled to Iraq and Syria between 2011 and 2015.

And US National Intelligence Director James Clapper says the number is now even higher. In February, he told the Senate Armed Services Committee "more than 36,500 foreign fighters -- including at least 6,600 from Western countries -- have traveled to Syria, since the conflict began in 2012."

And while the promenades of southern France may seem a world away from the war zone, the region -- and Omsen's childhood home, Nice, in particular -- has become a hotbed of jihadi recruitment.

Local imam Boubekeur Bekri says he knows people who "have been attracted by this massive lie of paradise."

Report: Number of ISIS foreign fighters increases 03:55

"They are transformed in a few weeks, or even in a few days -- it's like a bomb goes off ... ISIS can be very persuasive," he explains. "They take fragile people, and make them more fragile, and then they promise them paradise. They work to alienate and isolate these people."

Radicalization, he says, is "like a virus ... When a virus infects a lot of people, it's a pandemic and you can't use regular pills to cure it. You need bigger resources."

But despite a supposed crackdown -- France has been in a state of emergency since the Paris attacks in November last year -- the country's jihadi exodus is continuing unabated.