Explosion outside the Brussels Institute of Criminology

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An explosion outside Belgium's criminal institute was probably not caused by a bomb, the Brussels prosecutor's office has said.

The incident early on Monday is much more likely to be an arson attack on a crime laboratory, said a spokeswoman.

"It's probably not terrorism. It's a criminal act," said Ine Van Wymersch. "I cannot confirm that there was any bomb."

Damage at the National Criminology (Lab Geert Vanden Wijngaert/AP)

State broadcaster RTBF and other outlets reported that a car drove through a security barrier at the site about 2am local time, followed by an explosion which caused significant damage to the facility on the north side of the capital. Nobody was injured.

The institute assists and advises Belgium's justice authorities in carrying out their investigations.

(Geert Vanden Wijngaert/AP)

Belgium has been on high alert since co-ordinated suicide bomb attacks on Brussels' airport and subway killed 32 people on March 22.