"He appears to be the brains behind several planned attacks in Europe," the source told Reuters of Abdelhamid Abaaoud, adding he was investigators' best lead as the person likely behind the killing of at least 129 people in Paris on Friday.
According to RTL Radio, Abaaoud is a 27-year-old from the Molenbeek suburb of Brussels, home to other members of the militant Islamist cell suspected of having carried out the attacks.
Media in Belgium said Abaaoud had been involved in a series of planned attacks in Belgium foiled by the police last January.
At the time, Belgian police in the town of Verviers killed two men who opened fire on them during one of about a dozen raids against an Islamist group that federal prosecutors said was about to launch "terrorist attacks on a grand scale".
At the moment of the Verviers events, Abaaoud's cellphone was located in Greece, RTL said. While there was no clear link established, French prosecutors said fingerprints from one of the suicide bombers matched the prints of a man registered in Greece in October.

This undated image taken from a Militant Website on Monday Nov. 16, 2015 showing Belgian Abdelhamid Abaaoud. (Militant video via AP) Source: AP
In February of this year, Islamic State's online magazine Dabiq carried an interview with an Islamist bearing the name of Abdelhamid Abaaoud and boasting of having traveled through Europe unnoticed by security forces to organize attacks and procure weapons.
Abaaoud was also named in various media last year as the elder brother of a 13-year-old boy who left Belgium to become a child-fighter in Syria.
Interviewed by Belgian newspaper Het Laatste Nieuws earlier this year, their father Omar Abaaoud disowned his older son.
"Abdelhamid has brought shame to our family. Our lives are equally destroyed. Why would he want to kill innocent Belgians? Our family owes everything to this country," he said.
Following is a list of some of the seven attackers who died, as well as others named in the investigation.
Dead attackers:
Ismail Omar Mostefai, 29 (born Nov. 21, 1985), Frenchman of Algerian descent involved in Bataclan concert hall attack, lived for a time in Chartres area, southwest of Paris. Born in Courcouronnes, south of Paris. Source: prosecutor's office/judiciary sources. Name was put on French intelligence services' "S notice" in 2010 for reported radicalisation. An unnamed senior Turkish government official says Turkey contacted France about Mostefai in December 2014 and June 2015 but only got a return request for information on him after the Paris attacks.
Samy Amimour, 28 (born Oct. 15, 1987), involved in Bataclan attack. French, from Drancy, Saint Denis, north of Paris. Subject of international arrest warrant since late 2013. Had been under official investigation since October 2012 on suspicion of terrorism-related activity over a plan to go to Yemen. Source: Paris prosecutor's office statement.
Brahim Abdeslam, 31 (born July 30, 1984), brother of Salah Abdeslam, a key suspect still at large. French, resident of Belgium. Blew himself up at Comptoir Voltaire cafe in Paris. Source: French judiciary.
Bilal Hadfi, 20 (born Jan 22, 1995). Involved in Stade de France attack. Source: French judiciary.
Other:
Suicide bomber involved in Stade de France attack. Passport found beside dead body of kamikaze bomber carries name of Ahmad Al Mohammad, 25, (born Sept. 10 1990), from Idlib, northwest Syria. Passport being checked but fingerprints match up with print of a person registered under that name in Greece in October 2015. Source: French prosecutor's office.
Key suspects still at large:
Abdelhamid Abaaoud, 27, Belgian, suspected brains behind the attacks, apparently in Syria. Source: French judiciary official. RTL radio adds Abaaoud is a resident of Molenbeek district of Brussels. Also named by media last year as elder brother of a 13-year-old boy who left Belgium to become a fighter in Syria.
Salah Abdeslam, 26, French, born in Brussels, Sept. 15, 1989. Source: notice published by French police/police sources. Suspected of having rented black VW Polo car used in attacks in Paris.
Arrested:
Mohammad Abdeslam: brother of Salah and Brahim, arrested in Belgium. Source: French judiciary
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