PARIS (AFP) - A leading Belgian extremist in Syria who has boasted in videos about planning attacks in Europe and evaded police in his home country is being investigated as a possible mastermind of the Paris attacks, a French source said Monday.

Abdelhamid Abaaoud, a 28-year-old Belgian of Moroccan descent, has fought along the Islamic State (ISIS) group in Syria and has been on the run since police stormed a extremist cell in eastern Belgium's Verviers in January.

Investigators now see a link with the worst terror attacks in French history, which on Friday night led to the deaths of 132 people and were claimed by ISIS.

"It's a serious hypothesis," a French source close the investigation said, adding that Abaaoud is still living in Syria - large areas of which are ISIS-controlled.

Abaaoud, who in July was sentenced in absentia by a Belgian court to 20 years in prison, was in contact with at least one of the Abdeslam brothers.

Brahim Abdeslam was one of the suicide attackers in Paris, and his brother Salah is being hunted by police.

"Abaaoud and Salah Abdeslam knew each other and were involved in the same petty crimes," the French source said.

"This element and Abaaoud's fanaticism in Syria allow us to link him to the attacks," the source said, warning however that it was still "too early" to make a conclusion.

Earlier Monday, Belgium's Flemish-language newspaper De Standaard ran a story linking the bomber, Brahim Abdeslam, to Abaaoud.

Both Abdeslam, a Belgium-based Frenchman who blew himself up outside a bar on Boulevard Voltaire, and Abaaoud lived in the Brussels district of Molenbeek which has a reputation as a hotbed of Islamist militancy.

Abaaoud has been at large since a Belgian police raided an ISIS cell that he allegedly led in Verviers in January.

The cell had been planning to murder Belgian police officers days after the Paris attacks on the Charlie Hebdo satirical magazine and a Jewish supermarket.

In an interview with ISIS magazine Dabiq, which was published after he returned to Syria from Belgium after the raid, Abaaoud gloated about his escape.

"My name and picture were all over the news yet I was able to stay in their homeland, plan operations against them, and leave safely when doing so became necessary," said Abaaoud, who is identified in the magazine as Abu Umar al-Baljiki.

In the interview, he describes setting up a safe house along with two other extremists in Belgium - who were slain in the January raid - and obtaining weapons "while we planned to carry out operations against the crusaders".

Abaaoud's father Omar told La Derniere Heure Belgian newspaper in January that his son "brought shame" and "destroyed" the family.

"Why in the name of God, would he want to kill innocent Belgians? Our family owes everything to this country," the extremist's father said.

"We had a wonderful life, yes, even a fantastic life here ... Abdelhamid was not a difficult child and became a good businessman," the father was quoted as saying.

"But suddenly he left for Syria. I wondered every day how he became radicalised to this point. I never got an answer."