Violence spread across Stockholm on Wednesday, as large numbers of young people rampaged through the suburbs, throwing stones, breaking windows and destroying cars. Police in the southern city of Malmo said two cars had been set ablaze.
Media reports said a police station office was set on fire in Stockholm's southern suburb of Rågsved, where several people were also detained. No one was hurt and the fire was quickly put out.
Rioters defied a call for calm from the country's prime minister, going on the rampage after nightfall damaging stores, schools, a police station and an arts and crafts centre in the four days of violence.
"I think there is a feeling that we need to be in more places tonight," said Towe Hagg, spokeswoman for Stockholm police. One police officer was injured in the latest attacks and five people were arrested for attempted arson.
Selcuk Ceken, who works at a youth centre in the district of Hagsatra, said 40-50 youths threw stones at police and smashed windows before running away.
He said the rioters were in their 20s and appeared to be well-organised. "It's difficult to say why they're doing this," he said. "Maybe it's anger at the law and order forces, maybe it's anger at their own personal situation, such as unemployment or having nowhere to live."
The disturbances appear to have been sparked by the police killing a 69-year-old man wielding a machete in the suburb of Husby earlier this month, which prompted accusations of police brutality. The riots then spread to other poor Stockholm suburbs.
"We see a society that is becoming increasingly divided and where the gaps, both socially and economically, are becoming larger," said Rami Al-khamisi, co-founder of Megafonen, a group that works for social change in the suburbs. "And the people out here are being hit the hardest … We have institutional racism."
"The reason is very simple. Unemployment, the housing situation, disrespect from police," said Rouzbeh Djalaie, editor of Norra Sidan newspaper. "It just takes something to start a riot, and that was the shooting."
Djalaie said youths were often stopped by police in the streets for identity checks. During the riots, he said some police called local youths "apes".
The TV pictures of blazing cars has shocked a country proud of its reputation for social justice as well as its hospitality towards refugees from war and repression.
"I understand why many people who live in these suburbs and in Husby are worried, upset, angry and concerned," said the justice minister, Beatrice Ask. "Social exclusion is a very serious cause of many problems, we understand that."
After decades of practising the Swedish model of generous welfare benefits, Stockholm has reduced the role of the state since the 1990s, spurring the fastest growth in inequality of any advanced OECD economy.
While average living standards are still among the highest in Europe, successive governments have failed to substantially reduce long-term youth unemployment and poverty, which have affected immigrant communities worst.
Around 15% of the population is foreign-born, and unemployment among these stands at 16%, compared with 6% for native Swedes, according to OECD data.
Youth unemployment in Husby, at 6%, is twice the overall average across the capital.
The left-leaning tabloid Aftonbladet said the riots represented a "gigantic failure" of government policies, which had underpinned the rise of ghettos in the suburbs.
As unemployment has grown, the anti-immigrant Sweden Democrats party has risen to third in polls ahead of a general election due next year, reflecting many voters' worries that immigrants may be partly to blame.
While many of the immigrant population are from Nordic neighbours closely tied to Sweden by language or culture, the debate has tended to focus on poor asylum seekers from distant warzones.
Out of a total 103,000 immigrants last year, 43,900 were asylum seekers, almost 50% up from 2011. Nearly half of these were refugees from fighting in Syria, Afghanistan or Somalia, and will get at least temporary residency.
Among 44 industrialised countries, Sweden ranks fourth in the absolute number of asylum seekers, and second relative to its population, according to United Nations figures.
Policing in Stockholm has already been the focus of controversy this year, with allegations that police were picking out darker-skinned immigrants for identity checks on subway trains.