From a CNN report out of Brussels Belgium: 

Police detained six people in raids Thursday night as investigators raced to uncover the network behind this week’s terror attacks in the Belgian capital.

The Belgian federal prosecutor’s office didn’t provide details about who had been detained in the Brussels raids, why they had been apprehended or whether they will face charges.
“It will be decided tomorrow if these people will remain in custody,” the office said in a statement released late Thursday.
Two people were taken into custody in Brussels’ Jette neighborhood, one person was detained in a different part of the capital, and three people were in a vehicle in front of the federal prosecutor’s office when authorities apprehended them, public broadcaster RTBF reported.
So far, authorities have said they believe five men played a part in Tuesday’s bombings in Belgium that killed 31 people and injured 330. Three of the attackers are dead. Two of them could still be on the loose.
Also in a BBC article from Brussels:
Belgian police have arrested six people in Brussels as a major investigation continues into attacks that claimed 31 lives in the city on Tuesday.

The arrests were made in the Schaerbeek district. There is no word yet on the identities of the suspects or their possible connection to the attacks.

Separately, in France, a suspect who was plotting an attack has been arrested near Paris, officials said.

The Brussels bombings have been linked to last November’s Paris attacks.

So-called Islamic State (IS) has claimed the attacks in both Paris and Brussels.

The arrests in Schaerbeek were made late on Thursday, and followed house-to-house searches in the area.

Residents said they heard explosions during the police raids but the cause was unclear.

Also on Thursday evening, French police launched an anti-terror operation in Argenteuil, north-west of Paris, following the arrest hours earlier of a man suspected of planning an attack.

Interior Minister Bernard Cazeneuve said the suspected militant, of French origin, was in an “advanced stage” of a plot, adding that no connection had been made to either the Brussels or the Paris attacks.

Last November, 130 people died after militants opened fire and detonated bombs in a number of locations in the French capital.

You can read the rest of the BBC story here.