Four nights of rioting that has spread across Stockholm immigrant districts has raised fears that decades of integration efforts have gone dangerously awry.
The riots are believed to have been sparked by the police shooting last week of an elderly man in Husby - a low-income suburb only a short walk from the Kista Science Tower skyscraper, a symbol of the booming IT sector in one of Europe's wealthiest cities.
Prime Minister Fredrik Reinfeldt appealed for calm after the riots spread from northwestern to southern Stockholm. "It's important to remember that burning your neighbour's car is not an example of freedom of speech, it's hooliganism," he said.
One man was arrested on Wednesday on suspicion of setting fire to an arts-and-crafts centre in Husby.
"In the past 24 hours, around 30 cars have been set on fire... in the greater Stockholm area," said Kjell Lindgren, a spokesman for the Stockholm police.
Mobs torched a school and a nursery in two of Stockholm's most deprived areas, and threw rocks at firefighters, police officers and their vehicles, he said.
Reinfeldt said "everyone has to take responsibility for restoring calm".
On Tuesday, he waded into Sweden's heated debate on immigration by attributing some of the problems in Stockholm's low-income suburbs to failed integration.
"Sweden is a country that receives large groups from other countries. I'm proud of that," he said. But he added that "there is often a transition period between different cultures" that the government had sought to facilitate by improving Swedish language education.
Sweden has in recent years been one of Europe's top destinations for immigrants, both in absolute numbers and relative to its size. Around 15 per cent of the population is estimated to have been born abroad.
The riots have gripped Swedish media, and the anti-immigrant Sweden Democrats said the riots were the result of an "irresponsible" immigration policy.