The rally by the Nordic Resistance Movement in Goteborg, 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 Goteborg 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.
Goteborg was scarred by violent demonstrations in 2001 on the sidelines of a European Union summit.
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