Paris police banned a protest on Saturday against violence by the force, a week after France was rocked by riots sparked by the killing of a teenager in a suburb of the French capital.
The Paris police department said in a decision published on its website that it had banned the planned demonstration on the Place de la Republique over risks to public order, citing a "context of tensions".
French authorities and politicians including President Emmanuel Macron have denied institutional racism within the country's law enforcement agencies.
The police have come under scrutiny after the June 27 fatal shooting by a police officer of Nahel M at a traffic stop. The 17-year-old was driving a sports car without a licence.
Saturday's protest was called by the family of Adama Traore, a Black Frenchman who died in police custody in circumstances similar to the killing of George Floyd in the United States.
The demonstration against alleged police violence and racial discrimination was initially planned as a march in Beaumont-sur-Oise, another Paris suburb, where Traore died in 2016.
But this had already been banned by local authorities, citing an elevated risk to public order and security.
The ban was upheld by a court on Friday, prompting the call for a gathering in central Paris instead. Left-wing leaders, including the LFI parliamentary group chief Mathilde Panot, had said they would join the gathering.
It was not immediately clear whether the organisers would challenge the new ban by the Paris authorities.
Further demonstrations over Nahel's killing are planned in several major French cities over the weekend, including in Marseille and Strasbourg.
A policeman who prosecutors said acknowledged firing a lethal shot at Nahel is under formal investigation for voluntary homicide, equivalent to being charged under Anglo-Saxon law.
His lawyer has said the officer had aimed at the driver's leg but was bumped when the car drove off, causing him to shoot towards his chest, and had not intended to kill the teenager.
Separately, the French foreign ministry on Saturday denied a UN Committee on the Elimination of Racial Discrimination (CERD) allegation of racial discrimination and excessive use of force by French law enforcement officials.
The UN body had said on Friday that France should make it a priority to address "the structural and systemic causes of racial discrimination, including in law enforcement".
"Any accusation of systemic racism or discrimination by law enforcement in France is unfounded", the foreign ministry said, echoing similar statements it has made previously.