Attackers rammed a car through the gates of Belgium's crime institute early Monday and set fire to a lab containing crime scene samples, apparently in an effort to destroy evidence, Brussels prosecutors said.

As the blaze in the north Brussels suburb erupted, residents heard at least one explosion and Belgian media reported a bomb attack, but investigators said the noise was probably materials going up in flames.

Belgium has been on high alert since coordinated suicide bombings at the Brussels airport and subway on March 22 killed 32 people, and security forces remain on standby for another attack.

Prosecutors said five people were detained and taken in for questioning after the incident, which happened at about 2 a.m. 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," Van Wymersch said. She said the lab contains "sensitive information" being used in ongoing investigations.

The fire and damage were hampering the efforts of investigators to enter the scene, and she said it would take some time for them 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," Van Wymersch told reporters. "It is obvious that several individuals would have an interest in making elements in their justice file disappear."

Belgium's 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 Belgium in recent weeks amid a series of criminal knife and shooting attacks and two hoax anthrax attacks.

On Friday, one person was killed and at least four were injured in an accidental explosion at a sports center near the French border.

Over the weekend, Belgian Prime Minister Charles Michel announced new security plans to ease the load on the security services, including creating a new force to protect key buildings and the greater use of private security firms for concerts or sports events.

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John-Thor Dahlburg in Brussels contributed.