Prosecutors say the attackers rammed Belgium’s criminology institute with a car at about 2am local time before setting it ablaze.
The fire caused a blast but no casualties.
“The Brussels Prosecutor’s office opened an investigation on arson. We are clearly talking about a criminal act. The thesis of terrorism can not be confirmed yet… This location was not chosen randomly,’‘ said spokeswoman Ine Van Wymersch.
Five people arrested near the site following the blast have been released without charge.
It was initially reported by Belgium media that a bomb had exploded at the lab.
The country has been on high alert since March following the attacks on Brussels airport and the city’s metro which killed 32 people. (Euronews)