A bomb scare which forced an evacuation of the U.S. embassy in Brussels and the Belgian Defence Ministry on Wednesday turned out to be a false alarm, police said.

Hundreds of U.S. diplomats and ministry employees were evacuated from their buildings after a suspicious minivan was noticed parked nearby.

After around 45 minutes, during which major avenues of central Brussels were gridlocked with traffic, a bomb squad declared the vehicle safe and police gave the all clear.

Ilse Van de Keere, a police spokeswoman, said officers on a routine patrol were suspicious of the vehicle because it carried reproduction number-plates and had wires hanging loose inside.

A bomb disposal unit was called but discovered nothing suspect.

"In the end they found nothing unusual, but given the numerous visible wires and the fact that the car was very close to the U.S. embassy and several Belgian ministries, we didn't want to take any risks," Van de Keere told reporters.

"The bomb disposal operation is now over, and the police are making the final checks needed to reopen the roads."

The U.S. embassy compound is an easily identified and heavily secured complex not far from Brussels' Royal Palace. It backs on to a major road that circles the center of the city.