An incendiary bomb, which did not go off, was found on Friday morning near a building in Merksem, a district of the city of Antwerp, local police said.
The bomb, which was intended to cause a fire, was reportedly thrown on Thursday night, but did not explode.
Investigators will seek to determine whether the botched attack was linked to the drug trade.
Police have set up a security perimeter around the explosive device to allow the forensic laboratory to conduct a search for clues.
