Belgian prosecutors confirmed Monday that five more people have been arrested during a series of anti-terrorism raids as Brussels, a major European capital and home to the European Union, remains on lockdown under maximum alert for a third straight day.

The recent arrests bring the total number of people detained since police launched a major security operation on Sunday night to 21, with 16 of them already taken into custody, according to AFP.

"Following the operation 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.

"A total of 21 persons were arrested since yesterday. They are currently questioned by the police," the statement concluded.

The raids are aimed at shutting down a terrorist network which is suspected of planning an attack similar to the one which left 130 people dead in Paris 10 days ago, according to CNN.

"The worry is that there's another attack team out there, that they have explosives, that they have weapons," CNN security analyst Paul Cruickshank said Monday morning on CNN's "New Day." "Belgian police don't have a handle on where these guys are, and that's why they're shaking the tree so hard." 

No weapons or explosives were found, and around $27,500 in cash was seized during one of the raids.

Salah Abdeslam, reported to be the mastermind of the Paris attacks, was not among those arrested, which could serve to further undermine wavering confidence in the competence of Belgium's counter-terrorism agencies, according to the Guardian.

As the work week begins in Brussels, schools, shopping malls and the subway all remain closed. People were warned to avoid large gatherings while soldiers and police were out in force patrolling the streets.

In the meantime, France made good on its promise to retaliate against ISIS for the Paris attacks and launched its first airstrikes from a newly deployed aircraft carrier on Monday.