A gunman killed three people, including two police officers, in the Belgian city of Liege on Tuesday, a city official said.
The gunman was shot dead following the attack, public broadcaster RTBF reports.
The dead in Tuesday's attack included two police officers and a passer-by.
He reportedly shouted "Allahu akbar", or "God is great".
Gunman shoots police in Liege, four dead: Belgian media
The Belgium federal prosecutor's office told ABC news that it's taking over the investigation from a local Liege prosecutor because "There are elements that make us believe that it was a terror attack".
Prime Minister Charles Michel said only that "there was a serious incident".
A crisis center official in Belgium says that the situation around the shooting site in Liege is fully safe and has added that there is no reason to increase the terror threat level.
Mr Jambon said: "Our thoughts are with the victims of this terrible act".More news: Government set to eradicate mycoplasma bovis
Having stabbed them, prosecutor Philippe Dulieu said, the man then seized one of their handguns and shot both women dead before walking down the street and shooting dead a 22-year-old man who was sitting in the passenger seat of a parked vehicle. "We are in the process of establishing an overview of exactly what happened", Jambon wrote on Twitter.
He then fled and took hostage a housekeeper at Waha High School.
The Verviers cell also had links to Abdelhamid Abaaoud, the mastermind of the November 2015 Islamic State attacks on Paris that killed 130 people.
Belgium terror prosecutors have taken over the case.More news: Footage of violent N.J. beach arrest goes viral
"The event is classed as a terrorist incident", Dulieu said.
Liege, an industrial city close to the German border in a French-speaking region, was the scene of a shooting in 2011, when a gunman killed four people and wounded more than 100 others before turning the gun on himself.More news: Flash floods rush through Ellicott City, Maryland, trapping residents