Around 50 people were taking part in the event at the Gubbängen theatre in a southern suburb of the Swedish capital, organised by the Left Party and the Green Party.

“Three people were taken by ambulance to hospital,” the police said on its website, adding that it had no information about the injuries suffered.

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• Swedish party leaders condemn attack on anti-fascism meeting

According to the Expo anti-racism magazine, which had been invited to give a presentation at the event, “a group of Nazis” came into the theatre foyer just before the event was to begin and threw smoke bombs into the hall.

“The Nazis attacked visitors using physical violence… (and) vandalised the premises before throwing a type of smoke bomb that filled the entrance hall with smoke,” Expo wrote on its website.

“It’s terrible that a meeting organised by the left-wing party has been attacked,” said Prime Minister Ulf Kristersson, quoted by the TT news agency.

“This type of hateful behaviour has no place in our free and open society,” he said, adding that he had contacted the party’s leader to express his “deepest support”.

All of Sweden’s political parties denounced the assault as an “attack on democracy”, TT said.

Left Party leader Nooshi Dadgostar told public broadcaster SVT that an “open event, for equality among individuals” was “violently attacked by those who seemed to be Nazis”.

She also called on “all political forces” to fight the “far right that threatens our democracy”.