Rioting spread across Stockholm immigrant districts on Wednesday in a third night of unrest, raising fears that decades of integration efforts have gone dangerously awry.

The riots are believed to have been sparked by the deadly police shooting last week of an elderly man in Husby — a run down, low-income suburb that is only a short walk away from the Kista Science Tower skyscraper, a symbol of the booming IT sector in one of Europe’s wealthiest cities.

“I don’t know why they do it,” said Mehmet, an employee at a pizza restaurant in the suburb’s centre, where youths had broken into the eatery after smashing the windows with rocks.

Their spoils: nine or ten soft drinks.

Prime Minister Fredrik Reinfeldt has blamed the violence on “hooliganism” and 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 told news agency TT.

One man was arrested today 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.”

Yesterday, 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.

Some Husby residents felt that politicians and other commentators were reading too much into the issue.

“It’s got nothing to do with the 69-year-old,” said Reber Berry, a train driver.

Others pointed out that many of the rioters were in their early teens and had no first hand experience of issues like youth unemployment and discrimination.