A witness reported that the man had a Kalashnikov assault rifle. No one was reportedly injured in the incident. The shooter was targeting La Parisienne restaurant on Avenue Louise.
According to a spokesperson for the prosecutor's office, Ine Van Wymersch, it was not believed to be a terrorist attack. The motive of the attack is unclear.
"A witness saw a man shoot with a Kalashnikov-style weapon in the direction of the window of a restaurant on Avenue Louise", Ine Van Wymersch said.
"On the spot, the police found three bullet impacts. For now, we are not aware of any injuries," she added.
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Police officers are searching for the suspect and will try to identify the attacker as soon as possible, the prosecutor's office spokeswoman added. Ballistics experts have been sent to the scene.