Authorities have carried out a raid in southern Belgium linked to the Paris attacks but did not detain any suspects.
The raid in Sambreville, 80 kilometres (50 miles) south of Brussels and close to the French border, was carried out around noon on Thursday.
The area was cordoned off and a mobile lab was on place.
It came as a civil protection squad decontaminated several people as a precaution at the main Brussels mosque after a suspicious parcel arrived.
The person who opened the package discovered white powder and immediately contacted the authorities.
A specialised crew from the fire department was sent, witnesses at the scene said.
Fire brigade Captain Anne Wibin said 11 people underwent a precautionary decontamination until it could be exactly established what the powder is.
She said it will take six hours to analyse the powder, but it is not radioactive.