Key Paris attacks suspect Salah Abdeslam has told interrogators that he "wanted to blow himself up" at the Stade de France but changed his mind, Paris prosecutor Francois Molins told a Paris news conference.
"These first statements, which should be taken cautiously, leave a whole series of issues that Salah Abdeslam must explain," he added.
Abdeslam has been formally charged in connection with the November massacre, but will oppose his transfer to France, his lawyer said earlier.
However, defence lawyer Sven Mary told reporters at federal police headquarters in Brussels that Abdeslam "will refuse his extradition at this stage".
"He is cooperating with Belgian justice," he said.
"France is asking for his extradition. I can tell you that we will refuse the extradition to France."
Abdeslam, who was arrested after being wounded in a dramatic raid in central Brussels, has left Saint-Pierre hospital but authorities did not say where he had been taken.
In the wake of the arrest, Interpol has advised extra vigilance at Europe's borders as Abdeslam's capture may encourage any accomplices to flee.
Four other people were detained, Belgium's federal prosecutor said, adding that one of them was also on a wanted list.
Meanwhile, the family of Abdeslam is relieved that he is at least safe, his brother's lawyer said.
"Mohamed Abdeslam, who I have just talked to, asked me to say ... in the name of the family, that there is a sense of relief," lawyer Nathalie Gallant told RTBF television.
"Firstly, because Salah was taken alive. The family had hoped for that. Relief too that finally the manhunt is over because you must understand the family has been under constant pressure for the past four months."
The 26-year-old was taken from a Brussels hospital to appear before an examining magistrate in connection with his role in the November 13 attacks claimed by the Islamic State group and which left 130 dead in Paris.
He was arrested in Brussels' gritty Molenbeek neighbourhood, home to a large, mostly North African community where the family has lived for many years.
Belgian police had earlier announced they had found fingerprints belonging to Abdeslam at the scene of an apartment raided on Tuesday.
Another of his brothers, Brahim, blew himself up in the Paris attacks and was buried on Thursday in a Brussels cemetery where Mohamed Abdeslam led the funeral cortege.
He told reporters at the ceremony: "You can watch and write your stories but please, out of respect, no photographs."
Ms Gallant also acts for Abid Aberkan, who was arrested on Friday for sheltering Abdeslam in Molenbeek and charged with "participating in a terrorist group" and hiding a fugitive.