A Belgian judge on Tuesday ordered a man found with a chainsaw and a gun near the European Parliament to be detained for a week on charges of threatening an attack.
The arrest of the 32-year-old Slovakian on Monday sparked a bomb alert in central Brussels amid fears of Islamist attacks against police and public buildings.
The suspect, dressed in military fatigues, was detained Monday when he said he had wanted to meet European Parliament President Martin Schulz.
Prosecutors said Tuesday he was being kept in detention on charges of threatening an attack and possessing a prohibited weapon.
The suspect "has cooperated all through the investigation but he has not made any statement," the Brussels prosecutor's office said.
The incident comes as Belgium remains on high alert after police broke up a suspected jihadist cell said to have been on the point of carrying out an attack last month.
Police shot dead two men in that operation and rounded up several others they have linked to Islamist groups which have sent fighters to Syria and Iraq.
The Belgian crackdown came just days after Islamist gunmen killed 17 people in attacks on the Charlie Hebdo satirical magazine and a Jewish supermarket in Paris.