American officials are scrutinizing reams of intelligence data in an attempt to determine if there was anything that the US Intelligence Community could have known in advance about the terrorists and the coordinated attacks in Paris that killed 129 people and left 300 others hospitalized.

"We continue to assess the situation, but have nothing public to give you on the developing details," a US intelligence official told VICE News. "We have seen nothing that contradicts President [Francois] Hollande's assessment. Of course the IC [intelligence community] is working with its French counterparts and is scrubbing intelligence."

President Barack Obama convened a National Security Council meeting on Saturday afternoon before departing for the G20 Summit. The White House said the president discussed the Paris attacks and was briefed on the latest intelligence, which, "while noting that there was no specific or credible threat to the United States, reviewed our homeland security posture to ensure we are doing everything necessary to protect the American people."

"The president received a briefing on the active cooperation with our French counterparts on intelligence sharing and military action against ISIL, and reaffirmed that his team will remain in close contact with their French counterparts to be ready to provide any necessary assistance to French authorities as part of the investigation," the White House said, referring to the fight against the Islamic State. "The team reviewed the intelligence picture, noting that we had no information to contradict the initial French assessment of ISIL's responsibility."

Martin Reardon, a veteran FBI counterterrorism agent who currently serves as the vice president of the New York City-based security intelligence firm The Soufan Group, said it's possible the attacks were planned "under the radar" and that the terrorists avoided detection. But the men could have already been known to French law enforcement and intelligence officials, which was the case with Cherif and Said Kouachi, the brothers who attacked the offices of Charlie Hebdo magazine and killed a dozen staffers.

'What happened last night is long term — it's not going to stop. Americans have to understand that these attacks will continue to occur.'

Even so, "it doesn't mean you know what they're going to do," Reardon said in an interview with VICE News early Saturday morning from Abu Dhabi.

"Here's the issue, there are limited resources when it comes to the actual physical surveillance and then the electronic surveillance," Reardon said. "When you have electronic surveillance and you're picking up conversations are you reviewing those in real time, which means you have somebody sitting there dedicated to that one phone or that one email account and they're looking at every exchange? Or are they being collected and looked at later on? Or run through an algorithm that is looking for certain buzz words or communication with a specific individual? It's resource intensive and they can't look at everybody. If you have cells that are being very careful, it's less likely it's going to be picked up."

He said, "terrorists are not dumb." They have learned "what governments can and cannot do" with regard to surveillance.

Reardon said that while some US government officials may seek to cast blame for the intelligence failure in Paris on the leaks by Edward Snowden, the NSA whistleblower, and say "had a [certain surveillance program] been in place" the attacks could have been foiled, the reality is "there are very few examples where the US government has been able to show that because of this [surveillance] program we were able to thwart an attack."

"Al Qaeda in the late '90s stopped using satellite phones when they learned the US government could intercept 100 percent of their communications," said Reardon, who was formerly the chief of the FBI's 24/7 Terrorist Screening Operations Center. "Terrorist groups don't use emails like they used to. They're careful on phones. It is possible to do this under the radar."

US intelligence officials told VICE News FBI agents have been dispatched to Paris to assist with the investigation and to help French officials recover information from cell phones, computers and other electronic devices.

One of the key questions that French and US Intelligence officials will need to answer is whether the attackers were part of a "locally radicalized grassroots cell" that personally picked their targets, or were they given specific instructions and assistance from abroad. Reardon said it's clear that the simultaneous attacks across Paris showed that it was planned at least weeks in advance, and that the terrorists received some degree of military training.

"If you look at France in particular a number of foreign fighters over the past five years have gone to Syria and Iraq and other conflict zones in North Africa and Asia," he said. "Counterterrorism officials have been saying all along what happens when they return? Some we know about. But there are others you don't even know who have left. Most foreign fighters when they're done in the conflict zone they're done fighting. But a small percentage come back with combat experience and they are determined to mount an attack."

Reardon said the attacks Friday in Paris are noteworthy and significantly different than previous terrorist attacks in the West based on "the number of sites that were simultaneously attacked and the number of tactics and methods used."

"Multiple suicide bombings, a drive-by shooting that you don't see very often, and then the assault on a public venue where they took hostages," he said. "There were a number of different tactics used to get that maximum effect. Usually it's one or the other. These people obviously had gone through military training. There was significant preparation that went into this and it was done under the radar."

He said building the suicide vests and manufacturing the explosives and "to make them work" requires a degree of technical sophistication. Additionally, training likely entailed attending a concert or an event at the Bataclan to determine the venue's "weak points" for entry and how to keep people from escaping, studying the security screening process at Stade de France, and perhaps trying to get past security with an explosive device.

"To take the risk of going into [Stade de France] with a suicide vest and getting caught would compromise the entire operation," Reardon said. "So did they try doing this beforehand and did they get past security with something else? Were they monitoring what the security situation was like?"

He said the significance of a terrorist attack in a tourist city like Paris is that other terrorist groups now see this and say "'Hey we can do that and do it better in different cities.'"

'They can't look at everybody. If you have cells that are being very careful, it's not going to be picked up.'

While a city like New York could certainly be hit, it's different than other cities around the world because there is a robust counterterrorism force and it is "the most prepared." New York City can "dispatch thousands of police into the streets very quickly," Reardon said. "It doesn't mean an attack couldn't succeed, but they are probably the most prepared. And that takes millions and millions of dollars, which most cities can't afford to invest for something that may never happen."

Although the Islamic State has taken credit for the Friday's attacks, Reardon said it's important not to forget that Ayman al-Zawahiri, the current leader of al Qaeda, called for "lone wolf" attacks against the West, specifically the US, just a couple of weeks ago.

"The first matter is striking the West and specifically America in its own home, and attacking their interests that are spread everywhere," Zawahiri said in a videotaped message, according to SITE Intelligence Group, which monitors jihadist websites.

Reardon said there's a battle right now for followers between the Islamic State and al Qaeda for the global leadership, and the latter terrorist group and they may seek to try and carry out an even more spectacular operation.

One of the arguments made by some of the veteran intelligence officials who spoke with VICE News is that the Obama administration's strategy against the Islamic State, which relies heavily on drone strikes to take out its leadership, is depriving the US of valuable intelligence if they were captured instead.

Reardon agreed and said, "There's a very strong argument that we are missing out on intelligence" but the problem is "this is a political battle" and the Obama administration would rather not have to deal with issues such as where to hold the fighters and where and how to prosecute them.

Reardon noted that the attacks are an opportunity for the US to "look at how it wants to conduct its counterterrorism operations."

"Are we going to do it through wars and with these drone strikes? There's a strong argument that does nothing but increase the rage," he said.

Such a review does not appear to be on anyone's agenda. Instead, US lawmakers have called for a more aggressive response to the Islamic State. In a statement Saturday, Democratic Senator Dianne Feinstein, the co-chair of the Senate Intelligence Committee, said she believes "we need to further increase our efforts in Syria and Iraq directly and expand our support to partner nations in other countries where ISIL is operating … The fight is quickly spreading outside Iraq and Syria, and that's why we must take the battle to them."

"It has become clear that limited airstrikes and support for Iraqi forces and the Syrian opposition are not sufficient to protect our country and our allies," Feinstein said. "This is a war that affects us all, and it's time we take real action to confront these monsters who target innocent civilians."

But Reardon said while Friday's attacks are "shocking from a counterterrorism perspective," they shouldn't necessarily come as a surprise.

"Unless you're in a police state people are going to gather and they are going to be vulnerable," he said. "The bottom line is we have to realize what happened last night is long term — it's not going to stop. Americans have to understand that these attacks will continue to occur. Law enforcement will be able to foil some they are certainly not going to foil all of them. This is the new reality. It's not going to change anytime soon."