Police cordon off the scene of the triple fatalities in the city of Liege. AFP

An attack that killed two policewomen and a male bystander in the Belgian city of Liege is being treated as "terrorist murder," prosecutors said yesterday.

The gunman, identified as 31-year-old Benjamin Herman, is also suspected in the killing of a fourth person in Marche-en-Famenne on the eve of his rampage, prosecutors' spokesman Eric Van Der Sypt said.

"The facts are qualified as terrorist murder and attempted terrorist murder," Van Der Sypt said, referring also to the shootings that wounded four other police officers.

The assessment was based on a number of "first elements" from the investigation, including the modus operandi of attacking police with a knife and stealing their firearms, which the Islamic State has encouraged in online videos.

Van Der Sypt said they also based their argument on the fact he shouted "Allahu Akbar," or "God is greatest" in Arabic.

Finally, Van Der Sypt said, there were reports that the perpetrator had "been in touch with radicalized persons."