Far right groups involved in protest
Water cannon have been used to disperse hundreds of suspected far-right protesters gathered at the Place De La Bourse.
A March Against Fear had been due to take place at the square, which has become a shrine to the 28 victims of the city's twin attacks.
It was called off by the event organisers after Belgium's interior minister urged protesters not to attend, saying police were too stretched.
Hundreds of people were nevertheless gathered in the square to pay their final respects when they were joined by dozens of men, some in balaklavas, who made their way onto the steps of the Brussels Stock Exchange.
Members of the crowd unfurled a large banner with an anti-Islamic State message.
A number of the protesters were heard shouting nationalist and anti-immigrant slogans.
Police in Brussels carried out 13 new raids on Sunday, taking nine people into custody for questioning and releasing a further five.
Authorities also charged another man - who was shot by police at a tram stop on Saturday - with membership of a terror group.
It comes a day after a man identified as Faycal Cheffou was charged with terrorist murder, participation in a terrorist group and attempted terrorist killings.
Reports suggesting he may be the so-called "man in white", who fled the airport in Brussels after his bomb failed to detonate, have not been confirmed.
Two other men, pictured on CCTV moments before the attack, blew themselves up in the airport departure lounge.
An hour later another bomb exploded on a subway train as it was pulling out of the Molenbeek metro station.
More to follow.