Belgian police briefly used water cannon to control several hundred rowdy protesters in central Brussels on Sunday after they ignored an official call for marches to be postponed following Tuesday's bombings.
Amid fears of further attacks, officials wanted to give police the scope to focus on investigations which have widened to other countries, leading to the arrest of an Algerian in Italy and intelligence cooperation with Germany. Police carried out 13 new raids in Belgium itself.
Hundreds nevertheless gathered at the Bourse to express solidarity with the victims of the suicide bomb attacks at Brussels airport and on a rush-hour metro train. Thirty one people were killed, including three attackers, and hundreds more injured. Islamic State has claimed responsibility.
Most of the protests were peaceful but white-helmeted riot police used the water cannon against a group of protesters, many of whom local media described as right-wing nationalists, who burst onto the square chanting and carrying banners denouncing Islamic State.
"It is highly inappropriate that protesters have disrupted the peaceful reflection at the Bourse (stock exchange). I strongly condemn these disturbances," Prime Minister Charles Michel said according to Belga news agency.
Brussels Mayor Yvan Mayeur said the group were "scoundrels".
In and around Brussels and Antwerp, police carried out 13 new raids in connection with the attacks, with nine people questioned and five later released, the prosecutor's office said.
With links to the Paris attacks in November becoming clearer, and amid criticism that Europe has not done enough to share intelligence about suspected Islamist militants, cooperation appeared to be deepening.
Belgian press agency Belga said on Sunday prosecutors had charged a man in connection with a raid in Paris on Thursday that authorities say foiled an apparent attack plot.
