The only suspected participant in Nov. 13 Paris attacks to be captured alive has been cooperating with police investigators and is "worth his weight in gold", his lawyer said on Monday.

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 told public radio.

French investigator Francois Molins told a news conference in Paris on Saturday that Abdeslam, a French citizen born and raised in Brussels, 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 Islamic State; but he later backed out.

Abdeslam's lawyer Sven Mary said he would sue Molins for making the comment public, calling it a violation of judicial confidentiality. Molins, speaking in Brussels on Monday alongside his Belgian counterpart, insisted he had the right to make elements of the inquiry public in an "objective" manner.

Mary said Abdeslam, who is fighting extradition to France, 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," Mary told Belgian public broadcaster RTBF.

More operations planned?

As the only suspected participant or planner of the 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 Islamic State in Syria.  There would also be urgent interest in finding out what further attacks might be planned.

Belgian prosecutors said in a statement they were looking for 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 the news conference he was unsure of Laachraoui's role.

Some media suggested he may have been the group's "armourer" and 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 on Sunday that Abdeslam may have been plotting more operations drawing on weapons discovered in the apartment where the shootout occurred and a network of associates. Belgian public broadcaster RTBF said on Monday that police had found detonators in the flat.

Jambon said he could not confirm that further attacks were being planned, but that 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.

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.