A spokesman for Belgium's federal prosecutor's office says the person is under arrest but has refused to give any further details ahead of an official announcement due later Saturday.
The official spoke anonymously as he was not allowed to speak publicly. He also said that a suspect arrested earlier — identified only as Osama K. by authorities — was from Sweden, providing partial confirmation that the man is Osama Krayem from the Swedish city of Malmo.
Magnus Ranstorp, a counterterrorism expert at the Swedish National Defense College, says Krayem had previously posted photos from Syria on social media.