Abdelhamid Abaaoud, a 28-year-old Belgian of Moroccan descent, has fought along the Islamic State (IS) group in Syria and has been on the run since police stormed a jihadist 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 129 people and were claimed by IS.
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.
More From This Section
"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.
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 IS 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 IS's magazine Dabiq, which was published after he returned to Syria from Belgium after the raid, Abaaoud gloated about his escape.
In the interview, he describes setting up a safe house along with two other jihadists in Belgium -- who were slain in the January raid -- and obtaining weapons "while we planned to carry out operations against the crusaders.