Paris attacks suspect Salah Abdeslam was preparing attacks in Brussels before he was arrested, Belgian Foreign Minister Didier Reynders has suggested.
Abdeslam is being interrogated in Belgium following his arrest in a dramatic raid in Brussels on Friday.
Many weapons and a new terror network had been uncovered in the city, Mr Reynders told a foreign policy forum.
The Paris attacks, claimed by so-called Islamic State (IS), left 130 people dead and dozens injured.
Mr Reynders cited information that he said had come to light since Abdeslam's arrest.
"He was ready to restart something in Brussels," he told the German Marshall Fund of the United States meeting in the city.
"And it's maybe the reality because 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 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."
France has reinforced its border security and Interpol has warned that accomplices may try to flee across frontiers now that Abdeslam is in custody.
In another development, Abdeslam's lawyer, Sven Mary, said he planned to take legal action against Paris prosecutor Francois Molins for breach of confidentiality.
Mr Molins told reporters on Saturday that Abdeslam had admitted he wanted to blow himself up during the attacks on 13 November, but then changed his mind.
Mr Mary said he would take legal action against Mr Molins for breaching the confidentiality of the investigation.
The Belgian authorities have charged Abdeslam with terrorism offences.
The 26-year-old French national, born in Belgium, spent four months on the run.
He is fighting extradition to France, which could take up to three months, though Mr Mary says his client is co-operating with the Belgian authorities.
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 (1,600ft) 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.
Footage showed Abdeslam being bundled into a police car on Friday after a volley of gunfire. Alaaj was also injured during the arrests.
Prosecutors said Alaaj had travelled with Abdeslam to Germany last October, where his fingerprints were taken during an identity check.