The new arrests bring the total number of people detained since Belgian police launched major anti-terror raids on Sunday night to 21. The hunt for a militant suspected of involvement in the Paris attacks continues.
Belgian citizen Salah Abdeslam has not yet been found despite the large-scale police hunt on Sunday and Monday. He is suspected of playing a key role in the terror attacks in Paris that killed 130 people.
"Following the operations of last night, five more house searches were conducted in the Brussels region and two more in the Liege region. Five persons were arrested during these searches," the federal prosecutor's office said in a statement on Monday. The 21 detained persons were "currently questioned by the police."
During one of the searches, around 26,000 euros ($ 27,500) in cash were seized.
Authorities in Brussels are still warning of possible attacks like those in the French capital.
Prime Minister Charles Michel said the city would remain on Belgium's fourth and highest level of security threat, meaning the threat of a terrorist attack was "serious and imminent."
The metro, museums, schools, universities, nursery schools, many shops and cinemas stay shut on Monday in the usually bustling capital of the European Union.
Jambon: More than one suspected terrorist
Belgian Interior Minister Jan Jambon told RTL radio on Monday morning: "Apart from the closed metro and schools, life goes on in Brussels, the public sector is open for business today, many companies are open."
NATO said its headquarters in Brussels were open, but some staff had been asked to work from home and external visits had been canceled. Following the terror attacks in Paris on November 13, NATO raised its alert level.
EU institutions were also open, with soldiers patrolling outside.
Germany has also stepped up security along its border with Belgium, a German police spokesman told Reuters after media reports that suspect Abdeslam was spotted near the frontier.
However, the danger was not linked to Abdeslam alone, Belgian Interior Minister Jan Jambon told Flemish broadcaster VRT: "The threat is broader than the one suspected terrorist."
Schulz: No 'general suspicion' against Muslims
In the wake of the Paris terror attacks and the lockdown in Brussels, the head of the European Parliament, the German Social Democrat Martin Schulz, warned not to discriminate against Muslims.
"I think that social exclusion leads to radicalization," he stated. "If we don't manage to see Muslims as a normal part of our society, if we don't realize that 99 percent of all the Muslims in the world describe the 'Islamic State' as a monster (...), but place them under general suspicion because of IS, we act in the terrorists' interest."
To keep the young away from radical influences, the EU has to do more in its fight against youth unemployment, a problem Schulz described as the "scourge of our time."
Martin Schulz told German radio broadcaster Deutschlandfunk that he had spoken to many EU employees about the lockdown in Brussels. Those who have children said they were "worried." However, most of the people he talked to were "relatively calm," favoring preventive measures by the police.
das/kms (Reuters, AFP, dpa, KNA)