(CNN) Intelligence obtained by Western security agencies before the November 13 Paris attacks indicated as many as 60 ISIS fighters had been deployed by the group to Europe to carry out attacks on five cities and had already reached European soil, a senior European counterterrorism source told CNN.

The intelligence indicated the target cities included Paris, London, Berlin and a major population center in Belgium, according to the source. It also indicated Abu Mohammed al-Adnani , the head of ISIS' external operations efforts, was the key figure behind the ambitious plan, the source said. There was no indication the plan was to attack the cities simultaneously.

The source cautioned the threat stream was based on intelligence which was fragmentary and difficult to verify, and it was too vague to act on. In addition, there was no specific intelligence prior to the Paris attack on any moving parts of the plot.

French security forces move people in the area of Rue Bichat in the 10th District. A witness told BFMTV that firefighters were on the scene to treat the injured.

French security forces move people in the area of Rue Bichat in the 10th District. A witness told BFMTV that firefighters were on the scene to treat the injured.

Rescue workers and medics tend to victims at the scene of one of the shootings, a restaurant in the 10th District. Attackers reportedly used AK-47 automatic weapons in separate attacks across Paris, and there were explosions at the Stade de France.

Rescue workers and medics tend to victims at the scene of one of the shootings, a restaurant in the 10th District. Attackers reportedly used AK-47 automatic weapons in separate attacks across Paris, and there were explosions at the Stade de France.

People leave the Stade de France after explosions were heard near the stadium during a soccer match between France and Germany on Friday. Paris Deputy Mayor Patrick Klugman told CNN President Francois Hollande was at the match and was evacuated at halftime.

People leave the Stade de France after explosions were heard near the stadium during a soccer match between France and Germany on Friday. Paris Deputy Mayor Patrick Klugman told CNN President Francois Hollande was at the match and was evacuated at halftime.

French security forces rush in as people are evacuated in the area of Rue Bichat in the 10th District of Paris.

French security forces rush in as people are evacuated in the area of Rue Bichat in the 10th District of Paris.

Spectators gather on the field of the Stade de France after the attacks. Explosions were heard during the soccer match between France and Germany.

Spectators gather on the field of the Stade de France after the attacks. Explosions were heard during the soccer match between France and Germany.

A wounded man is evacuated from the Stade de France in Saint-Denis, outside Paris.

A wounded man is evacuated from the Stade de France in Saint-Denis, outside Paris.

Police secure the Stade de France in Saint-Denis, north of Paris, following explosions during the soccer match between France and Germany.

Police secure the Stade de France in Saint-Denis, north of Paris, following explosions during the soccer match between France and Germany.

A riot police officer stands by an ambulance near the Bataclan concert hall in central Paris.

A riot police officer stands by an ambulance near the Bataclan concert hall in central Paris.

A woman walks past police and firefighters in the Oberkampf area of Paris.

A woman walks past police and firefighters in the Oberkampf area of Paris.

A medic tends to a wounded man following the attacks near the Boulevard des Filles du Calvaire.

A medic tends to a wounded man following the attacks near the Boulevard des Filles du Calvaire.

Wounded people are evacuated outside the scene of a hostage situation at the Bataclan theater in Paris on November 13.

Wounded people are evacuated outside the scene of a hostage situation at the Bataclan theater in Paris on November 13.

Rescuers evacuate an injured person on Boulevard des Filles du Calvaire, close to the Bataclan concert hall in central Paris.

Rescuers evacuate an injured person on Boulevard des Filles du Calvaire, close to the Bataclan concert hall in central Paris.

A body, covered by a sheet, is seen on the sidewalk outside the Bataclan theater.

A body, covered by a sheet, is seen on the sidewalk outside the Bataclan theater.

Spectators embrace each other as they stand on the playing field of the Stade de France stadium at the end of a soccer match between France and Germany in Saint-Denis, outside Paris, on November 13.

Spectators embrace each other as they stand on the playing field of the Stade de France stadium at the end of a soccer match between France and Germany in Saint-Denis, outside Paris, on November 13.

Spectators invade the pitch of the Stade de France stadium after the international friendly soccer match between France and Germany in Saint-Denis.

Spectators invade the pitch of the Stade de France stadium after the international friendly soccer match between France and Germany in Saint-Denis.

A survivor of the terrorist attack in the Bataclan is assisted following terror attacks, November 13. The violence at the Bataclan, which involved a hostage-taking, resulted in the highest number of casualties of all the attacks.

A survivor of the terrorist attack in the Bataclan is assisted following terror attacks, November 13. The violence at the Bataclan, which involved a hostage-taking, resulted in the highest number of casualties of all the attacks.

Rescuers evacuate an injured person near the Stade de France, one of several sites of attacks November 13 in Paris. Thousands of fans were watching a soccer match between France and Germany when the attacks occurred.

Rescuers evacuate an injured person near the Stade de France, one of several sites of attacks November 13 in Paris. Thousands of fans were watching a soccer match between France and Germany when the attacks occurred.

Forensics are working in the street of Paris after the terrorist attack on Friday, November 13. The words "horror," "massacre" and "war" peppered the front pages of the country's newspapers, conveying the shell-shocked mood.

Forensics are working in the street of Paris after the terrorist attack on Friday, November 13. The words "horror," "massacre" and "war" peppered the front pages of the country's newspapers, conveying the shell-shocked mood.

A woman is evacuated from the Bataclan theater early on November 14.

A woman is evacuated from the Bataclan theater early on November 14.

Victims of the shooting at the Bataclan concert venue in central Paris are evacuated to receive medical treatment on November 14.

Victims of the shooting at the Bataclan concert venue in central Paris are evacuated to receive medical treatment on November 14.

Police officers patrol the area around Notre Dame cathedral in Paris on November 14.

Police officers patrol the area around Notre Dame cathedral in Paris on November 14.

A man with blood on his shirt talks on the phone on November 14. He is next to the Bataclan theater, where gunmen shot concertgoers and held hostages until police raided the building.

A man with blood on his shirt talks on the phone on November 14. He is next to the Bataclan theater, where gunmen shot concertgoers and held hostages until police raided the building.

Police, firefighters and rescue workers secure the area near the Bataclan concert hall on November 14.

Police, firefighters and rescue workers secure the area near the Bataclan concert hall on November 14.

Medics evacuate an injured woman on Boulevard des Filles du Calvaire near the Bataclan early on November 14.

Medics evacuate an injured woman on Boulevard des Filles du Calvaire near the Bataclan early on November 14.

Security forces evacuate people on Rue Oberkampf near the Bataclan concert hall early on November 14.

Security forces evacuate people on Rue Oberkampf near the Bataclan concert hall early on November 14.

Shoes and a bloody shirt lie outside the Bataclan concert hall on November 14. Most of the fatalities occurred at the Bataclan in central Paris.

Shoes and a bloody shirt lie outside the Bataclan concert hall on November 14. Most of the fatalities occurred at the Bataclan in central Paris.

Forensic police search for evidence inside the Comptoir Voltaire cafe after the attacks.

Forensic police search for evidence inside the Comptoir Voltaire cafe after the attacks.

Police are out in force November 14 near La Belle Equipe, one of the sites of the terror attacks.

Police are out in force November 14 near La Belle Equipe, one of the sites of the terror attacks.

A forensic scientist works near a Paris cafe on Saturday, November 14, following a series of coordinated attacks in Paris the night before that killed scores of people. ISIS has claimed responsibility.

A forensic scientist works near a Paris cafe on Saturday, November 14, following a series of coordinated attacks in Paris the night before that killed scores of people. ISIS has claimed responsibility.

"In terms of ambition, it also just pointed towards something we already knew. ISIS had hardly made it a secret it sought to target Europe," said the senior European counterterrorism source.

In the year before the Paris attacks, Adnani had threatened the European countries supporting the anti-ISIS coalition in a series of audio messages, making specific references to France and Belgium. And in January 2015, Belgian police broke up a major ISIS plot in Belgium coordinated by Abdelhamid Abaaoud , who later became the ringleader of the Paris attacks.

Adnani is top target

The source said Western intelligence agencies believe Adnani is at the heart of ISIS' international attack planning. "As far as we're concerned, he is top of our target list," the source said.

The source said that the lack of specific intelligence on any moving parts of the Paris plot has caused consternation, because it is rare for any plot to fly completely under the radar. In most attacks that have gotten through, Western security agencies had picked up at least some specific chatter on planning, which they later realized related to the attack, the source said.

After the Paris attacks, new attention was focused on the fragmentary intelligence indicating 60 ISIS operatives had been deployed to Europe.

"The worry has been that if, say, 20 were involved in the Paris attacks, there might be 40 or so still out there," the source said.

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Western intelligence agencies are worried that ISIS may plot an even more ambitious attack. Alain Winants, the former head of the Surete de l'Etat, Belgium's domestic intelligence agency, told CNN, "A lot of secret services are fearing now that what has happened in Paris could happen again, but simultaneously by several groups, in several different countries, which would of course have an immense impact."

'How many lions?'

On Sunday ISIS, in a new issue of its French language magazine, quoted similar concerns other officials have expressed in French media reports, raising the specter of simultaneous attacks in several European countries, including France. "How many of our lions have entered (Europe). Ten? Fifty? One Hundred? With God's Will you'll soon find out," the magazine stated.

Last week there were reports that the Paris ringleader himself had spoken of belonging to a group of 90 who made the trip to Europe, a figure not far off the number in the intelligence reports.

The claims were made in a French radio interview by a woman who said she alerted French police to Abaaoud's location in Paris after picking him up in a wooded area near Saint-Denis, along with her friend, Abaaoud's cousin Hasna Aït Boulahcen.

Photos: World reacts to Paris attacks Photos: World reacts to Paris attacks President Barack Obama, French President Francois Hollande, second from right, and Paris Mayor Anne Hidalgo arrive at the Bataclan, site of one of the Paris terrorists attacks, to pay their respects to the victims after Obama arrived in town for the COP21 climate change conference early on Monday, November 30, in Paris. Hide Caption 1 of 40 Photos: World reacts to Paris attacks The Eiffel Tower in Paris is illuminated in the French national colors on Monday, November 16. Displays of support for the French people were evident at landmarks around the globe after the deadly terrorist attacks in Paris on Friday, November 13. Hide Caption 2 of 40 Photos: World reacts to Paris attacks People hold hands as they observe a minute of silence in Lyon, France, on November 16, three days after the Paris attacks. A minute of silence was observed throughout the country in memory of the victims of the country's deadliest violence since World War II. Hide Caption 3 of 40 Photos: World reacts to Paris attacks French President Francois Hollande, center, flanked by French Prime Minister Manuel Valls, right, and French Education Minister Najat Vallaud-Belkacem, center left, stands among students during a minute of silence in the courtyard of the Sorbonne University in Paris on November 16. Hide Caption 4 of 40 Photos: World reacts to Paris attacks A large crowd gathers to lay flowers and candles in front of the Carillon restaurant in Paris on Sunday, November 15. Hide Caption 5 of 40 Photos: World reacts to Paris attacks A man sits next to candles lit as homage to the victims of the deadly attacks in Paris at a square in Rio de Janeiro on November 15. Hide Caption 6 of 40 Photos: World reacts to Paris attacks People light candles in tribute to the Paris victims on November 15 in Budapest, Hungary. Hide Caption 7 of 40 Photos: World reacts to Paris attacks People gather outside Notre Dame Cathedral in Paris on November 15 for a national service for the victims of the city's terror attacks. Hide Caption 8 of 40 Photos: World reacts to Paris attacks People write messages on the ground at Place de la Republique in Paris on November 15. Hide Caption 9 of 40 Photos: World reacts to Paris attacks People pray during a candlelight vigil for victims of the Paris attacks at a church in Islamabad, Pakistan, on November 15. Hide Caption 10 of 40 Photos: World reacts to Paris attacks French golfer Gregory Bourdy passes a peace symbol for the Paris victims during the BMW Shanghai Masters tournament November 15 in Shanghai, China. Hide Caption 11 of 40 Photos: World reacts to Paris attacks A man offers a prayer in memory of victims of the Paris attacks at the French Embassy in Tokyo on November 15. Hide Caption 12 of 40 Photos: World reacts to Paris attacks A woman holds a candle atop a miniature replica of the Eiffel Tower during a candlelight vigil Saturday, November 14, in Vancouver, British Columbia. Hide Caption 13 of 40 Photos: World reacts to Paris attacks Front pages of Japanese newspapers in Tokyo show coverage and photos of the Paris attacks on November 14. Hide Caption 14 of 40 Photos: World reacts to Paris attacks An electronic billboard on a canal in Milan, Italy reads, in French, "I'm Paris," on November 14. Hide Caption 15 of 40 Photos: World reacts to Paris attacks The Eiffel Tower stands dark as a mourning gesture on November 14, in Paris. More than 125 people were killed in a series of coordinated attacks in Paris on Friday. People around the world reacted in horror to the deadly terrorist assaults. Hide Caption 16 of 40 Photos: World reacts to Paris attacks Lithuanians hold a candlelight vigil in front of the French Embassy in Vilnius, Lithuania, on November 14. Hide Caption 17 of 40 Photos: World reacts to Paris attacks Thousands gather in London's Trafalgar Square for a candlelit vigil on November 14 to honor the victims of the Paris attacks. Hide Caption 18 of 40 Photos: World reacts to Paris attacks A woman lights candles at a memorial near the Bataclan theater in Paris on November 14. Hide Caption 19 of 40 Photos: World reacts to Paris attacks A man places a candle in front of Le Carillon cafe in Paris on November 14. Hide Caption 20 of 40 Photos: World reacts to Paris attacks A woman holds a French flag during a gathering in Stockholm, Sweden, on November 14. Hide Caption 21 of 40 Photos: World reacts to Paris attacks Nancy Acevedo prays for France during the opening prayer for the Sunshine Summit being held at Rosen Shingle Creek in Orlando, Florida on November 14. Hide Caption 22 of 40 Photos: World reacts to Paris attacks French soldiers of the United Nations' interim forces in Lebanon observe the national flag at half-staff at the contingent headquarters in the village of Deir Kifa on November 14. Hide Caption 23 of 40 Photos: World reacts to Paris attacks A couple surveys the signature sails of the Sydney Opera House lit in the colors of the French flag in Sydney on November 14. Hide Caption 24 of 40 Photos: World reacts to Paris attacks A woman places flowers in front of the French Consulate in St. Petersburg, Russia, on November 14. Hide Caption 25 of 40 Photos: World reacts to Paris attacks Candles are lit in Hong Kong on November 14 to remember the scores who died in France. Hide Caption 26 of 40 Photos: World reacts to Paris attacks A woman lights a candle outside the French Consulate in Barcelona, Spain, on November 14. Hide Caption 27 of 40 Photos: World reacts to Paris attacks Britain's Prince Charles expresses solidarity with France at a birthday barbecue in his honor near Perth, Australia, on November 14. Hide Caption 28 of 40 Photos: World reacts to Paris attacks The French national flag flutters at half-staff on November 14 at its embassy in Beijing. Hide Caption 29 of 40 Photos: World reacts to Paris attacks Dutch Prime Minister Mark Rutte after a speech on November 14 in The Hague following the attacks. Hide Caption 30 of 40 Photos: World reacts to Paris attacks Japanese Prime Minister Shinzo Abe becomes emotional after his speech on the French attacks during the opening ceremony of a Japanese garden in Istanbul, Turkey, on November 14. Hide Caption 31 of 40 Photos: World reacts to Paris attacks A woman mourns outside Le Carillon bar in the 10th district of Paris on November 14. The attackers ruthlessly sought out soft targets where people were getting their weekends underway. Hide Caption 32 of 40 Photos: World reacts to Paris attacks People lay flowers outside the French Embassy in Moscow on November 14. Hide Caption 33 of 40 Photos: World reacts to Paris attacks Mourners gather outside Le Carillon bar in the 10th district of Paris on November 14. "We were listening to music when we heard what we thought were the sounds of firecrackers," a doctor from a nearby hospital who was drinking in the bar with colleagues told Le Monde. "A few moments later, it was a scene straight out of a war. Blood everywhere." Hide Caption 34 of 40 Photos: World reacts to Paris attacks People attend a vigil outside the French Consulate in Montreal. Prime Minister Justin Trudeau offered "all of Canada's support" to France on Friday, November 13, in the wake of the attacks. Hide Caption 35 of 40 Photos: World reacts to Paris attacks Police show a heightened presence in Times Square in New York on November 13, following the terrorist attacks in Paris. Hide Caption 36 of 40 Photos: World reacts to Paris attacks People light candles at a vigil outside the French Consulate in Montreal on November 13. Hide Caption 37 of 40 Photos: World reacts to Paris attacks University of Nevada, Las Vegas, fans observe a moment of silence for the victims of the terrorist attacks in Paris before a basketball game November 13. Hide Caption 38 of 40 Photos: World reacts to Paris attacks The house lights are shut off and scoreboard dark as Boston Celtics players pause for a moment of silence for the Paris victims before an NBA basketball game against the Atlanta Hawks in Boston on November 13. Hide Caption 39 of 40 Photos: World reacts to Paris attacks People light candles at a vigil outside the French Consulate in Montreal on November 13. Hide Caption 40 of 40

The woman said Abaaoud bragged to her during a taxi ride that the 90-strong group had traveled without official papers and included Syrian, Iraqi, French, German and British nationals who were now scattered around the greater Paris area.

CNN reported in December that a female "walk-in" had provided the key tip that led French police to a residence where Abaaoud was staying in the Saint-Denis area. Her account also matched an official confidential witness statement viewed by CNN.

In the months since the Paris attack there have been several terrorism alerts in Europe based on intelligence chatter, in cities including Brussels, Belgium; Hanover, Germany; Geneva, Switzerland; Vienna, Austria; and Munich, Germany.