The accomplice was named as Najim Laachraoui, 24 — previously known by the false name Soufiane Kayal which he used to travel to Hungary in September with Saleh Abdeslam, the key suspect who was finally arrested in a dramatic raid on Friday.
Laachraoui, who also travelled to Syria in February 2013, is still on the run.
French President Francois Hollande, who has said he wants Abdeslam extradited as quickly as possible, was due to hold his first formal meeting with relatives of the 130 Paris victims on Monday afternoon.
“The president, in light of recent events, will update them on what is happening,” the presidential palace said.
Investigators hope Abdeslam’s arrest in Brussels on Friday, in which he was wounded in the leg, will give new leads on the attacks claimed by the Islamic State (ISIS / ISIL) terrorist group.
Abdeslam, the last known survivor of the group that carried out the attacks, was found just around the corner from his family home in the gritty Brussels neighborhood of Molenbeek, where several other of the attackers hailed from.
Belgium has faced heavy criticism for failing to keep tabs on radicals there, AFP reported.
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