"He was ready to restart something in Brussels," said Reynders, speaking at the German Marshall Fund's Brussels Forum. "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."
The investigation also showed more people were involved in the November 13 Paris attacks than first thought, he said.
"After the terror attacks in Paris, I said to one TV channel in the U.S. that we were searching for around 10 people with heavy weapons. We have far more than that since November, and not only in Belgium but also in France," he said. " ... For the moment we have found more than 30 people involved in the terrorist attacks in Paris, but we are sure there are others."
Speaking in Brussels, Belgian Interior Minister Jan Jambon told CNN that Abdeslam's dramatic capture Friday
, following a four-month manhunt, was a major coup, but investigations were not over.
"I think it's a big blow, because he is one of the most wanted foreign fighters in Europe. But I'm very aware the network is not cleared, so we have to continue the actions and continue the investigation," he said.
His comments were reiterated by Belgian State Security Chief Jaak Raes, who told CNN Belgian affiliate VTM News on Sunday that it was "of the utmost importance that Abdeslam was captured alive, because we can now try to reconstruct the entire scenario."
That was crucial in order "to see to what extent the intelligence services can learn lessons from the information that is gleaned," he said.
He warned that the threat posed by ISIS to Europe was far from over, saying: "We know that a number of people are possibly on their way to Western Europe, with the intention of conducting an attack -- to, with the 'jihad mentality,' do damage to Western democracy. We need to stay very vigilant about that."
Authorities have said nine terrorists killed 130 people with guns and bombs in Parisian restaurants, shops and a concert venue the night of November 13.
Paris prosecutor Francois Molins has said Abdeslam had a key role in planning the attacks.
Charged with participation in terrorist murder
Belgian federal prosecutors said in a statement Saturday that Abdeslam, a Belgium-born French citizen, had been charged
with participation in a terrorist murder and with taking part in the activities of a terrorist organization.
The statement did not specify which terror group, but ISIS has claimed it was responsible for the Paris carnage.
Monir Ahmed Alaaj, also known as Amine Choukri -- the other man wounded in a gunbattle during Friday's raid in the Brussels suburb of Molenbeek
-- faced the same charges.
Of the three others detained in the operation, one was charged with participating in a terror group's activities and hiding criminals, and another with hiding criminals. The third was freed without being charged.
Did he stay in Belgium?
Jambon expressed surprise that Abdeslam, who is being held a high-security prison in Bruges, Belgium, had been found in Brussels, as authorities had believed that he might have left the country.
He said that investigators did not know whether Abdeslam had been in Belgium for the entire four months he was on the run, or whether he had traveled.
Jambon said he hoped that as a result of Abdeslam's arrest, authorities would be able to piece together the facts of the preparations for the horrific attacks and identify the network of individuals involved.
"There has to be (a) network -- also logistics network, also supporters -- helping him, and this is something we have to look (at) closer," he said.
Abdeslam fighting extradition
It may take three months to extradite Abdeslam, 26, to France, Paris prosecutor Molins said at a press briefing Saturday.
Abdeslam is cooperating with investigators but is fighting extradition, his lawyer, Sven Mary, told reporters.
Belgian Prime Minister Charles Michel said authorities in his country will do their best to arrange for the extradition "as soon as possible."
Molins said authorities have interviewed Abdeslam once and are still trying to confirm his role in the attacks.
Investigators think Abdeslam may have been the driver of the black Renault Clio that dropped off three suicide bombers near the Stade de France, one of the attack sites.
Did Abdeslam plan to use suicide belt?
His DNA was found on a discarded suicide belt found on a Paris street after the attacks, investigators have said.
Molins said Abdeslam has told investigators that he planned to blow himself up at the Stade de France but simply backed down. However, the prosecutor said he was suspicious of that statement.
Molins reminded reporters that in a communique issued by ISIS following the Paris attacks, the terror group mentioned the commissioning of an attack in the 18th district of the French capital.
That's why Abdeslam's statement "must be taken with precaution," Molins said.
"Investigations must determine if a suicide attack by Salah Abdeslam was supposed to take place in the 18th district," Molins said.
Abdeslam's lawyer, Mary, told Belgian public broadcaster RTBF Sunday that he intended to file a complaint over Molins' remarks on the case.
Mary said that by revealing information at a news conference from Abdeslam's interrogation, the Paris prosecutor was violating the secrecy of the investigation, RTBF reported.
After the attacks, Abdeslam is believed to have called friends to take him to Belgium. They passed through police checkpoints, but Abdeslam had not yet been identified as a suspect and they were allowed to continue on their way.
Abdeslam's fingerprints and DNA allegedly were found on Wednesday when police raided a Brussels apartment. One person was killed in that raid and two people escaped.
The man killed by a special forces sniper was Mohamed Belkaid, an Algerian who used the name Samir Bouzid
. He is believed to have directed the Paris attackers via calls from Belgium.
Belkaid helped Abdeslam travel prior to the attacks, a Belgian senior counterterrorism official told CNN in January.
Authorities believe he was using the apartment as a hideout following the Paris attacks, according to the official.
An intense manhunt resulted in Abdeslam's arrest.
Molenbeek has 'foreign fighter problem'
The impoverished Brussels suburb of Molenbeek, where Abdeslam was arrested after Friday's gunbattle, has a reputation as a hotbed for jihadism
Members of its large, predominantly Muslim population -- many of them immigrants from North Africa -- have been linked to terror plots and attacks.
Last fall, Belgian Justice Minister Koen Geens said more needs to be done to address what he called Belgium's "foreign fighter problem" in the suburb.
In the immediate aftermath of the Paris attacks, authorities detained numerous people there. Police continued to conduct operations in Molenbeek into Saturday morning.
Jambon said Sunday that his country's counterterror operations had already disrupted ISIS activities in Europe and the flow of aspiring foreign fighters going to Syria had decreased.
But he reiterated that changing an entrenched ideology takes time.
French officials on Saturday praised the police action that led to Abdeslam's capture. Interior Minister Bernard Cazeneuve called it "an important blow to the terrorist organization Daesh in Europe," using another name for ISIS.
"This is not the end of the fight that we are leading relentlessly against terrorism," Cazeneuve said. "We need to maintain our vigilance to be ahead of the threat."