Investigators: Multiple ISIS plots being planned in Europe

Updated 4:54 PM EDT, Thu March 24, 2016
In this image provided by the Belgian Federal Police in Brussels on Tuesday, March 22, 2016 of three men who are suspected of taking part in the attacks at Belgium's Zaventem Airport. The man at right is still being sought by the police and two others in the photo that the police issued were according to a the Belgian Prosecutors 'probably' suicide bombers. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (Belgian Federal Police via AP)
PHOTO: Belgian Federal Police via AP
In this image provided by the Belgian Federal Police in Brussels on Tuesday, March 22, 2016 of three men who are suspected of taking part in the attacks at Belgium's Zaventem Airport. The man at right is still being sought by the police and two others in the photo that the police issued were according to a the Belgian Prosecutors 'probably' suicide bombers. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (Belgian Federal Police via AP)
Now playing
02:08
Search continues for unidentified Brussels suspect
An unidentified traveler runs through the smoke filled terminal at Brussels Airport after explosion rocked the terminal Tuesday morning.
PHOTO: Ralph Usbeck/AP
An unidentified traveler runs through the smoke filled terminal at Brussels Airport after explosion rocked the terminal Tuesday morning.
Now playing
00:59
Brussels under attack
Nidhi Chaphekar, 41, was injured in the second blast at Brussels' Zaventem Airport on March 22, 2016 suffering burns and embedded metal to many areas of her body. A photo taken by Georgina journalist Ketevan Kardava shortly after the twin blasts came to sum up the tragedy of the attacks for many around the globe.
PHOTO: Ketevan Kardava/AP/Dominique Van Heerden/CNN
Nidhi Chaphekar, 41, was injured in the second blast at Brussels' Zaventem Airport on March 22, 2016 suffering burns and embedded metal to many areas of her body. A photo taken by Georgina journalist Ketevan Kardava shortly after the twin blasts came to sum up the tragedy of the attacks for many around the globe.
Now playing
02:28
Terror victim says iconic image brought hope
Belgium Brussels attacks arrests morgan lkl        _00010621.jpg
PHOTO: AFP/Getty Images
Belgium Brussels attacks arrests morgan lkl _00010621.jpg
Now playing
03:07
Several arrests made in Brussels terror attacks
utah teen mason wells belgium attack newday_00000000.jpg
PHOTO: CNN
utah teen mason wells belgium attack newday_00000000.jpg
Now playing
01:47
Teen survivor describes airport horrors
detainee to isis mclaughlin pkg _00034816.jpg
detainee to isis mclaughlin pkg _00034816.jpg
Now playing
03:57
Is he behind the Paris and Brussels attacks?
Gail and her husband LT. COL. Kato Martinez
PHOTO: Martinez Family
Gail and her husband LT. COL. Kato Martinez
Now playing
02:56
Remembering Gail Martinez
This handout photo released on April 7, 2016 by the Belgian federal police at the demand of the Brussels' king prosecutor shows grabs of security footage of the third suspect from the Brussels airport attack on March 22.
Belgian prosecutors on April 7 launched a fresh appeal for help to find a suspected third attacker in last month's bombings at Brussels airport, releasing new video footage and pictures of the so-called "man in the hat". / AFP PHOTO / BELGIAN FEDERAL POLICE AND BELGA / Handout / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / BELGA / BELGIAN FEDERAL POLICE " - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS

HANDOUT/AFP/Getty Images
PHOTO: BELGIAN FEDERAL POLICE/AFP/AFP/Getty Images
This handout photo released on April 7, 2016 by the Belgian federal police at the demand of the Brussels' king prosecutor shows grabs of security footage of the third suspect from the Brussels airport attack on March 22. Belgian prosecutors on April 7 launched a fresh appeal for help to find a suspected third attacker in last month's bombings at Brussels airport, releasing new video footage and pictures of the so-called "man in the hat". / AFP PHOTO / BELGIAN FEDERAL POLICE AND BELGA / Handout / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / BELGA / BELGIAN FEDERAL POLICE " - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS HANDOUT/AFP/Getty Images
Now playing
03:04
New video shows Belgian terror attacker leaving airport
brussels bomb us missing boyfriend eisenman_00002016.jpg
PHOTO: Emily Eisenman
brussels bomb us missing boyfriend eisenman_00002016.jpg
Now playing
03:20
Georgia woman's boyfriend is missing in Brussels
worldwide lights display Belgium flag cnn orig_00002730.jpg
worldwide lights display Belgium flag cnn orig_00002730.jpg
Now playing
00:54
Monuments around the world light up for Brussels
scared muslim Saima Mohsin pkg_00010314.jpg
scared muslim Saima Mohsin pkg_00010314.jpg
Now playing
02:48
Muslim man fears backlash after Brussels attacks
sebastien bellin father speaks brussels attack ac intv_00003406.jpg
PHOTO: Facebook/Sebastien Bellin
sebastien bellin father speaks brussels attack ac intv_00003406.jpg
Now playing
01:57
Father of Brussels attack survivor speaks to CNN
Nidhi Chaphekar, right, a 40-year-old Jet Airways flight attendant from Mumbai, and another unidentified woman after being wounded in Brussels Airport in Brussels, Belgium, after explosions were heard. The Indian flight attendant who was injured in the Brussels airport blasts is in stable condition and recovering, her airline Jet Airways said Friday, March 25, 2016. Chaphekar suffered burns and fractured her foot in the explosions on Tuesday. She has been treated at a hospital near Brussels.
PHOTO: Ketevan Kardava/AP
Nidhi Chaphekar, right, a 40-year-old Jet Airways flight attendant from Mumbai, and another unidentified woman after being wounded in Brussels Airport in Brussels, Belgium, after explosions were heard. The Indian flight attendant who was injured in the Brussels airport blasts is in stable condition and recovering, her airline Jet Airways said Friday, March 25, 2016. Chaphekar suffered burns and fractured her foot in the explosions on Tuesday. She has been treated at a hospital near Brussels.
Now playing
01:45
Video timeline: They saw the Brussels attacks
voices from belgium pkg_00004402.jpg
voices from belgium pkg_00004402.jpg
Now playing
02:12
Why are some Belgians leaving for war in Syria?
brussels explosions richard medic witness intv train station aftermath es_00013319.jpg
PHOTO: RTL Belgium
brussels explosions richard medic witness intv train station aftermath es_00013319.jpg
Now playing
01:48
Victims on ground after Brussels subway blast
PHOTO: @sindhleak
Now playing
04:08
Airport explosions witness: I saw victims on stretchers

Story highlights

Investigators believe the Brussels ISIS cell was planning a larger attack

ISIS has released a video urging its fighters in the West to carry out more attacks

(CNN) —  

Investigators are aware of multiple additional ISIS plots in Europe possibly linked to the Paris and Brussels networks that are in various stages of planning.

A combination of electronic intercepts, human sources and database tracking indicates several possible targets had been picked out by the ISIS operatives over the last few months since the Paris attacks, according to U.S. counterterrorism officials.

Since the attacks earlier this week, information found in a raided apartment, including maps, indicated other potential targets had been chosen, one of the sources said.

According to a senior Belgian counter-terrorism official, investigators believe the Brussels ISIS cell were composed of two teams who were planning a larger attack or series of attacks in Belgium at a later date. After police discovered Salah Abdeslam’s hiding place on Tuesday last week, investigators believe the second team, including suspected bomb-maker Najim Laachraoui, accelerated their timetable. They believe the second team consisted of the Bakraoui brothers and at least two others now on the run.

RELATED: Brussels attack: Man wanted in subway bombing

Investigators believe the first team was composed of Salah Abdeslam, a still-to-be identified accomplice taken into custody last Friday at the same time and Mohammed Belkaid, the suspected commander of the Paris and Brussels attack cell, according to the official.

Belkaid was shot dead during the firefight at Abdeslam’s hiding place last week after Belkaid provided covering fire so Abdeslam could flee the building, the Belgian source said. Police recovered an ISIS flag, a Kalashnikov, detonators, and ammunition at the safehouse, suggesting that Belkaid and Abdeslam’s team were planning gun and bomb attacks in Brussels like the same network had carried out in Paris. An ISIS flag was also recovered at the cell’s bomb factory in Schaerbeek, where the airport attackers set off from early Tuesday morning to launch their attacks.

The office of the Belgium’s prime minister would not answer CNN queries about the information.

Officials fear there are dozens of potential and known ISIS operatives still in Europe they’re concerned about and some of them may overlap with the Paris and Brussels attackers. One of the sources says plots haven’t been disrupted either because the information about the plots is too fragmentary or because investigators are trying to gather more intelligence. The source also stressed that the situation with the plots is very fluid and can change very quickly depending on the opportunity for the operatives some of whom have been trained by ISIS in Syria and Iraq.

Another official cautioned that there are multiple threat streams but not all get verified.

ISIS has released a video compiled using the group’s file footage, urging its fighters in the West to carry out more attacks.

“Intel doesn’t come in a neat form answering the who, what, where, when and why,” the official said. “We rarely are operating with a full utility belt.”

Other U.S. counterterrorism officials say there was chatter before the Brussels attacks indicating something was about to happen, but nothing specific enough to indicate where and when the attacks were going to happen.

“There is not that calm in between the storms we used to see,” said one U.S. official, who said typically one would expect there would be some time after an attack where others regrouped.

Officials say some of the other attacks they have been concerned before with specific times and places picked out did not pan out, but the sources cautioned ISIS followers are opportunistic and flexible if a planned attack doesn’t get executed.

“There’s evidence these guys are floating around in Europe and haven’t been rounded up yet and hope to launch an attack,” one official said, adding, “there’s a constant drumbeat and fear something else is going to happen.”

The concern was reflected in a State Department alert warning U.S. citizens traveling to Europe that terrorists continue to plot near term attacks.

It reflected a wider concern about the growing number of ISIS devotees who have been to Syria and Iraq and since returned. Ahead of the Paris attacks, Western intelligence received fragmentary information that ISIS external operations division dispatched 60 operatives to hit five cities, including Paris, London, Berlin, a major city in Belgium and another city. Paris mastermind Abdelhamid Abaaoud boasted of some 90 ISIS operatives already in Europe.

On Wednesday, the top Democrat on the House Intelligence Committee said there are a “large number” of such fighters back in Europe.

“Potentially hundreds,” said Rep. Adam Schiff, D-California, in an interview that aired on “The Situation Room” with CNN’s Wolf Blitzer. “If you include both foreign fighters that have returned from the fight as well as people that didn’t leave for the fight but in communication … with ISIS, it could well reach those numbers.”

The director of the FBI said Thursday that ISIS adherents returning to Europe are a continued concern.

“For almost three years now were very much worried about people around the glove we worry who travel to Syria and gets the worst kind of training and then flow back out, and it’s especially a problem in Europe. And so, this is a manifestation of that problem and I don’t think and doesn’t reflect greater skill or organization on ISIS’s part,” Director James Comey said.

CNN’s Elise Labott contributed to this report.