The coordinated nature of Friday`s deadly attacks across Paris points to an organized terrorist group, with ISIS the chief suspect as it looks to extend its reach globally, according to security experts.

No-one has claimed responsibility (at the time of writing) for the carnage that left at least 153 dead -- including 112 at the Bataclan concert venue in the center of the city.

But with a steady flow of radicalized foreign fighters traveling to places like Syria and then returning -- in addition to the considerable number of homegrown ISIS sympathizers in many European countries -- the militant Islamic organization is finding it easier to support and encourage these kind of attacks, experts say.

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"The French are overwhelmed by the numbers of people they`re having to monitor," said CNN terrorism analyst Paul Cruickshank.

"They`ve opened surveillance files into more than 5,000 Islamic extremists throughout the country. There have been more than a thousand French nationals traveling to Syria and Iraq. They know of 250 that have come back, and that`s just the number they`re aware of."

He pointed to a terror plot that was thwarted in Belgium in January, when security services uncovered a huge cache of weapons -- as well as police uniforms -- suggesting a possible attack on a sensitive site there.

"Intelligence officials there and in the United States have told me that plot was directed by the top leadership of ISIS in Syria," he said.

"This is a group that is increasingly getting into the international terrorism business. I think all these different events of the past few weeks have really illustrated this: More than 100 killed during anattack in Ankara -- ISIS suicide bombers -- the attack in Beirut, 40-50 killed, ISIS bombers that claim for taking down that Russian Metrojet airliner. It goes on. ISIS is pivoting towards international terrorism."

Sleepers

The fact the attacks in Paris all happened within 30 minutes suggested it was long-planned and there was some kind of command and control structure, according to Michael Weiss, the co-author of "ISIS: Inside the Army of Terror."

"That`s not to sat it`s coming out of ISIS HQ in Raqqa," he told CNN. "One of the things to keep in mind is the that the Caliphate has expanded in a way that many have not foreseen. It`s not necessarily taking up more terrain in Syria and Iraq, but it is getting these affiliates -- getting these sleepers -- essentially to declare allegiance and to conduct their own operations."

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While the gunmen and bombers picked a number of "softer" targets in the French capital -- a concert hall and restaurants -- other analysts believe the attack on the Stade de France was the real statement of intent.

"There`s a tremendous amount of symbolism when you have France playing Germany -- this is the national sport of France, this is where you`ll have a tremendous amount of people gathered there and watching on television, hearing the explosions go off," said CNN Political Commentator Buck Sexton.

"To explode suicide vests outside of there is really to strike at the heart of France when the entire country is watching. The entire country heard those explosions as they went off.

They would have thought `what was that?` So as soon as the news started to break, there would have been a ripple effect."

Propaganda

Cruickshank said the next challenge was the emergence of a major ISIS propaganda video if they eventually do take credit for the Paris attacks.

"Just recently, they (ISIS) instructed all their recruits, all their operatives on the ground, to film everything,` he said. "They say there`s no point launching these kinds of attacks if you don`t film them."

So how will France react?

According to Sexton, there will be a "quite a response" from France. "They`re already done airstrikes in Iraq and Syria. They`ll go with more of that I think. There`s also a U.S. presence on the ground in Syria -- that will likely increase."

He said France has shown it is capable of unleashing its fury.

And this is exactly the tone President Francois Hollande has taken.

Speaking from outside the Bataclan concert hall late Friday, he vowed France would be "ruthless" in its response.

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