COPENHAGEN, Denmark (AP) — Police said at least 50 people were detained Saturday during a right-wing demonstration in Sweden’s second-largest city that left one police officer and several others injured.

The rally by the Nordic Resistance Movement in Gothenburg, 400 kilometers (248 miles) southwest of Stockholm, featured an estimated 600 people marching in formation in all-black outfits. Some wore helmets and held shields, while others hoisted the movement’s green-and-white flags.

Police had posted flyers before the event warning people not to act in a way reminiscent of German Nazis demonstrations in the 1930s and 1940s.

NMR, which promotes an openly anti-Semitic doctrine, originally sought to pass near a downtown synagogue during the march, which coincided with Yom Kippur, Judaism’s holiest day of the year. But Swedish courts intervened and shortened the route to less than one kilometer (0.6 mile.) The rally’s ending time also was shortened to avoid clashing with a nearby soccer game.

Counter-demonstrators threw fireworks and attempted several times to break police lines, allegedly to confront NMR members, who also tried to get past riot police. Several were detained on suspicion of rioting, police said.

“Stones, bottles and sticks were also thrown at us,” police spokesman Hans Lippens said.

Police offered to shuttle NMR members away in buses after they were circled by riot police on a Gothenburg square, preventing them from completing their march. Police said the move was meant to keep both sides apart.

The NMR later demanded that its leader who had been detained, Simon Lindberg, be released before they would leave the square.

Counter-demonstrators threw rocks at police outside the Liseberg amusement park, which reportedly shut down its main entrance.

Some 20 people, mostly Danes and Germans, were stopped as they arrived in Sweden to take part in the demonstration.

“As a democracy, we should do much more to oppose Nazism and extremism,” Swedish Prime Minister Stefan Lofven told reporters Friday at an EU summit in Tallinn.

Gothenburg was scarred by violent demonstrations in 2001 on the sidelines of a European Union summit.

Members of the Jewish community, which typically is under tight security, said ahead of the march that they were worried about harassment and physical threats from the marchers, said Allan Stutzinsky, chairman of the Gothenburg Jewish community.

People affiliated with the Nordic Resistance Movement were responsible for anti-Semitic threats that led to the shuttering in April of the Jewish community center in Umea, a city in northeastern Sweden, according to Stutzinsky.

A community center is part of the synagogue complex in Gothenburg.

“The threat against us is always large, and it becomes even larger when they are marching,” Stutzinsky told JTA, adding that left-wing counter protesters may also be a threat to Jews.

Swedish Jews face anti-Semitism both from the nationalist far right as well as the far left, whose strong criticism of Israel sometimes veers into anti-Semitism.

Stutzinsky noted that Holocaust survivors and their descendants are members of the Gothenburg Jewish community.

“Almost all of our members have some sort of connection to the Holocaust,” he said. “It is obvious that it is upsetting for them to see, and maybe hear, Nazis protest close to the synagogue, when everyone is there at the Yom Kippur service,” he added, speaking before the route of the march was moved away from the synagogue.

The community is not opposed to the group’s right to march, he said, but to the event’s location and timing.

Stutzinsky said the planned march did not represent an isolated incident.

“One would have thought that World War II was an effective vaccination against anti-Semitism. But it didn’t last that long, now it’s back again,” he said.

“We have anti-Semitism here again like in the 1930s. We thought Europe had learned its lesson, but that’s apparently not the case.”