At least one police officer was injured in Berlin on Saturday when about 500 counter-activists shouting “Nazis out” clashed with an equal number of neo-Nazis commemorating the 31st anniversary of the suicide of Nazi officer Rudolf Hess in prison.

Many of the far-right activists, dressed in red and white, raised the red, white and black flag, a symbol of German barbarism. One group carried a sign saying: I have no regrets: the National Socialists of Berlin’.

About 2,300 police were on duty to prevent violence at the Berlin event and a separate march of fewer than 50 people in the Berlin suburb of Spandau, where Hess, a former Hitler chancellor, served a life sentence after being tried for war crimes in Nuremberg.

A broad mix of counter-demonstrators organized non-violent sit-ins at the intersections along the march route in the Berlin neighborhood of Lichtenberg, while others gathered to shout against the neo-Nazi demonstrators.

“There were reports of injuries when some stones and bottles were thrown by counter-demonstrators at right-wing protesters,” Berlin police spokesman Thilo Cablitz told reporters. “At least one police officer was injured. But as the event continues we will still be compiling the numbers”.

Germany has harsh laws prohibiting the public use of Nazi symbols, such as swastikas, but the far right has been strengthened in recent years after the arrival of more than a million immigrants, mostly Muslims, from 2015. While far-right activity remains a marginal phenomenon in Germany, it has been behind high-profile crimes.