Swedish police have made arrests after reports that scores of black-clad men rampaged through central Stockholm attacking people after handing out leaflets that threatened violence against foreigners.
The incident on Friday night, which was followed by an anti-refugee protest on Saturday, highlights growing tensions in a country of 10 million people that received 163,000 asylum seekers last year.
It also came a day after a 22-year old female worker was stabbed to death in a centre for unaccompanied asylum-seeking minors in the southwest of the country.
Interior Minister Anders Ygeman called the incident on Friday, as well as the anti-refugee demonstration on Saturday, which local media said later resulted in some scuffles with counter-demonstrators, worrying.
"Racist groups are spreading hate and violence in our streets. This has to be met with force," Ygeman said in a statement.
Swedish newspapers said that according to witnesses a number of people had been attacked by the gang on Friday, who they reported to be hooligans associated with local football teams.
One witness told the Aftonbladet newspaper that he had seen a group of men beating people in the middle of the capital's busy central Sergels torg square. 
Police said three arrests were made on Saturday, the Reuters news agency reported.
The police also said one man had been arrested on Friday night for punching a plain clothes officer and another for carrying a knuckleduster, but the extent of assaults on immigrants was not clear.
'Our duty'
The leaflets handed out on Friday, which police said were also posted to Swedish social media, said: "When Swedish streets are no longer safe for ordinary Swedes it is our DUTY to fix the problem ... The police have amply shown that it lacks the means to rein them in and we now see no alternative than for us to mete out the punishment they deserve."
The Swedish government said this week it was likely to deport between 60,000 and 80,000 of last year's applications for refugee status in a move that drew criticism from rights groups. 
More than 35,000 unaccompanied minors sought asylum in Sweden last year, roughly half of them registered as 16 or 17 years old. More than 23,000 of them came from Afghanistan.