The only suspected participant in November's Paris attacks to be captured alive has been cooperating with police investigators and is "worth his weight in gold", his lawyer has said.
Belgium's Interior Minister Jan Jambon said the country was on high alert for a possible revenge attack following the capture of 26-year-old Salah Abdeslam in a flat in Brussels on Friday.
"We know that stopping one cell can ... push others into action. We are aware of it in this case," he said.
French investigator Francois Molins said Abdeslam had admitted to investigators he had wanted to blow himself up along with others at the Stade de France on the night of the attack claimed by the so-called Islamic State.
Abdeslam's lawyer Sven Mary said he would sue Mr Molins for making the comment public, calling it a violation of judicial confidentiality.
Mr Mary said Abdeslam was now fully cooperating with investigators.
"I think that Salah Abdeslam is of prime importance for this investigation. I would even say he is worth his weight in gold.
"He is collaborating. He is communicating. He is not maintaining his right to remain silent," Mr Mary said.
As the only suspected participant or planner of the 13 November Paris attack in police custody, Abdeslam would be seen by investigators as a possible major source of information on others involved, in support networks, finance and links with IS in Syria.
There would also be urgent interest in finding out what further attacks might be planned.
In total, 130 people were killed in a series of coordinated shootings and bombings across Paris last year, with the highest death toll at the Bataclan.
Belgian prosecutors said they were looking for Abdeslam's accomplice Najim Laachraoui, 25, using the false name of Soufiane Kayal.
His DNA had been found in houses in Belgium used by the Paris attackers.
Lead Belgian investigator Frederic Van Leeuw told a news conference that he was unsure of Laachraoui's role.
Some media suggested he may have been the group's "armourer" and Mr Leeuw confirmed he had travelled to Hungary in September in a car rented by Abdeslam and in the company of a third man, who was killed in a shootout with police in Brussels last Tuesday.
Belgian Foreign Minister Didier Reynders said Abdeslam may have been plotting more operations in the Forest district of Brussels due to a weapons find in that location and a network of associates that was uncovered.
Mr Jambon said he could not confirm that, but it was a possibility.
"After 18 months of dealing with this terrorist issue, I have learned that when the terrorists and weapons are in the same place, and that's what we saw in Forest, we are close to an attack.
"I'm not saying it is evidence. But yes, there are indications," he said.
Mr Reynders said Belgium and France had so far found around 30 people involved in the gun and bomb attacks on bars, a sports stadium and a concert hall in the French capital.