Police have arrested a man who was seen on security footage next to Khalid El Bakraoui, the suicide attacker who detonated a bomb in the Brussels metro, De Standaard newspaper reported on Friday.
The federal prosecutor's office did not confirm the arrest.
De Standaard newspaper said the man, whom it did not name, was arrested after a policeman recognized him from the security footage.
Khalid El Bakraoui, 27, who blew himself up on a crowded rush hour train, is the brother of Brahim El Bakraoui, who detonated a bomb at Brussels Airport an hour earlier.
The joint attacks killed at least 31 people and wounded 316.
Public broadcaster RTBF meanwhile reported police detained a seventh person in the district of Forest following six arrests late on Thursday.