Attackers rammed a car through the gates of Belgium's crime institute and set fire to a lab containing crime scene samples, apparently in an effort to destroy evidence.
Residents heard at least one explosion as the blaze erupted in a north Brussels suburb and Belgian media reported a bomb attack, but investigators said the noise was probably materials going up in flames.
Prosecutors said five people were detained for questioning and released without charge following the incident at about 2am on Monday in Neder-Over-Heembeek. No one was injured.
"It's probably not terrorism. It's a criminal act," said Ine Van Wymersch, a spokeswoman for the Brussels prosecutor's office.
"I cannot confirm that there was any bomb."
The forensic facility assists Belgium's justice authorities in carrying out their investigations and the lab contains DNA samples found at crime scenes.
"The location was not chosen randomly," said Ms Van Wymersch.
She said the lab contains sensitive information being used in ongoing investigations.
The fire and damage hampered the efforts of investigators to enter the scene, and she said it would take some time to establish exactly what had been destroyed.
"The laboratory does thousands of analyses each year, so we don't know what damage has been done yet," said Ms Van Wymersch.
"It is obvious that several individuals would have an interest in making elements in their justice file disappear."
Belgium has been on high alert since suicide bombings at the Brussels airport and subway killed 32 people on March 22, and security forces remain on standby for another attack.
The police and army have been deployed in large numbers since suicide bombers attacked Paris last November, leaving 130 dead. Many of the attackers had links to Belgium.
Tensions have also been running high in recent weeks amid a series of criminal knife and shooting attacks and two hoax anthrax attacks.
One person was killed and at least four were injured on Friday in an accidental explosion at a sports centre near the French border.
Belgian prime minister Charles Michel announced new plans to ease the load on the security services at the weekend.
They include creating a new force to protect key buildings and using more private security firms for concerts or sports events.
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules hereComments are closed on this article