Five people have been held and questioned over a fire at Brussels' criminology institute, a spokeswoman for the city's prosecutors says.
Arsonists set fire to Belgium's National Institute of Criminology in Brussels earlier on Monday, causing an explosion but no casualties.
"Five people were detained in the vicinity and are being heard," the spokeswoman, Ine Van Wymersch, told a news conference.
When asked whether the attack could be terrorism she said: "It is a path we are looking down. But certainly not the first one we are thinking about.
"We are thinking more of deliberate arson by organised crime. We have no indications that it was terrorism."
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Belgium has been on high alert since Islamist attacks over the past year.
Several attackers entered the site of the institute by car early on Monday and went into the wing of the building where the laboratories are located, prosecutors said.
More details about how the fire was started were not yet known as the building was still too dangerous to enter.
The institute is linked to the Belgian ministry of justice and carries out forensic investigations in criminal cases, its director said.
Belgium has been on high alert since a March 22 attack on the Brussels airport and subway killed 32 people.
