French President Francois Hollande is to meet relatives of those killed in November’s jihadist attacks in Paris, in the wake of the capture of alleged organiser Salah Abdeslam.
Support groups for victims say they hope his capture in Brussels on Friday will help in the search for the truth.
So-called Islamic State said it carried out the attacks, that left 130 dead.
Belgian officials say Abdeslam, who is still being interrogated, was planning more attacks in Belgium.
The BBC’s Lucy Williamson in Paris says that for those who lost relatives in the attacks, relief at Salah Abdeslam’s arrest is quickly turning to hunger for the information he might provide.
“We hope [his arrest] will help us in the search for truth” read the message from one support group set up after the November attacks.
But our correspondent says that Mr Hollande’s meeting with survivors and victims’ families comes amid recrimination that, four months after the attacks, they are being ignored.
Earlier this month, Georges Salines, who lost a daughter in the Bataclan theatre during the attack, said he had written to Francois Hollande to ask for such a meeting, but was “stunned” to be told that there was no time in the president’s schedule.
France has tightened security at its borders after the arrest of the man dubbed Europe’s most-wanted fugitive.
Mr Hollande has said that the number of people involved in the terrorist network is much larger than originally thought and that he wants Abdeslam transferred to France as soon as possible to face prosecution.
But Abdeslam’s lawyer, Sven Mary, has reacted angrily to French involvement, in particular comments by Paris prosecutor Francois Molins that Abdeslam had admitted he wanted to blow himself up during the attacks on 13 November, but then changed his mind.
Mr Mary told French media on Sunday: “I don’t understand why a prosecutor in Paris has to communicate at this stage on an investigation in Belgium.”
He said Abdeslam was “worth gold. He is collaborating, he’s communicating, he is not using his right to remain silent”.
Belgian Foreign Minister Didier Reynders has suggested Abdeslam was preparing attacks in Brussels before he was arrested.
“We have found a lot of weapons, heavy weapons, in the first investigations and we have found a new network around him in Brussels,” Mr Reynders told a foreign policy forum.
Mr Reynders said the number of suspects had risen markedly since the November attacks.
“We are sure for the moment we have found more than 30 people involved in the terrorist attacks in Paris, but we are sure there are others.”
The Belgian authorities have charged Abdeslam with terrorism offences.
The 26-year-old French national, born in Belgium, spent four months on the run.
Abdeslam is believed to have fled shortly after the November attacks, returning to the Molenbeek district of Brussels.
He is being held at a high-security jail in the Belgian city of Bruges.
Investigators believe he helped with logistics, including renting rooms and driving suicide bombers to the Stade de France.
The subject of a massive manhunt, Abdeslam was arrested about 500m (1/3 of a mile) from his home in Molenbeek. His brother, Brahim, was one of the Paris attackers who blew himself up on 13 November.
Another man arrested at the same time as Salah Abdeslam on Friday, Monir Ahmed Alaaj, has also been charged with participation in terrorist murder and the activities of a terrorist group, Belgian prosecutors say.
The raid came after Abdeslam’s fingerprints were found in a flat in another Brussels district, Forest, raided on Tuesday.