The organizers of a demonstration against the "Islamization of Europe" failed to have a ban by the mayor of Brussels lifted on Friday, when a Brussels court said it was not competent to rule on their appeal.
Organizers said however that the demonstration will go ahead in Brussels on September 11, the anniversary of attacks on the United States, despite the ban.
"There will still be a demonstration and a big one," said Anders Gravers, one of the protest's supporters.
Gravers, the founder of the Stop Islamization of Denmark party, denied he and fellow organizers were racist, although far-right groups across Europe have voiced support for their cause.
He said some 20,000 people were expected to come from across Europe to Brussels, seat of most European Union institutions.
A spokesman for the Brussels mayor, who feared the protest would threaten public order, said the police were aware of the situation and ready to intervene on Tuesday if necessary.