Stockholm police called in reinforcements from across Sweden to quell a possible sixth straight night of riots in the capital's immigrant-dominated suburbs as Britain and the United States warned against travelling to the hotspots.
Nearly a week of riots have put Sweden's reputation as an oasis of peace and harmony at risk.
The unrest has also sparked a debate among Swedes over the integration of immigrants, many of whom arrived under the country's generous asylum policies, and who now make up about 15 percent of the population.
"We will be getting reinforcements from Gothenburg and Malmoe tonight," police spokesman Kjell Lindgren said, referring to the country's second and third largest cities.
He would not disclose how many additional police officers were due to arrive.
Another police spokesman, Lars Bystroem, told the Swedish news agency TT that he had never before experienced unrest that lasted so long and was spread over such a wide area.
The nightly riots have prompted Britain's Foreign Office and the US embassy in Stockholm to issue warnings to their nationals, urging them to avoid the affected suburbs.
Firefighters were dispatched to 70 fires the night between Thursday and Friday, extinguishing torched cars, dumpsters and buildings, including three schools and a police station, the fire department wrote on Twitter. This was down from 90 blazes the night before.
Parents and volunteer organisations who have patrolled the streets in recent nights have helped decrease the intensity of the unrest, Lindgren said.
He said 13 people had been arrested overnight, bringing to 29 the total arrests since the start of the riots on Sunday.
Police, who have so far concentrated on putting out fires, are beginning to round up people suspected of criminal acts, according to TT.
"Even if we don't intervene, we regularly make video recordings and get information from the public. That way we can get people a couple of days later," said Bystroem, the police spokesman, to TT.
The troubles had begun in the suburb of Husby, where 80 percent of inhabitants are immigrants, triggered by the fatal police shooting of a 69-year-old Husby resident last week after the man wielded a machete in public.
Local activists said the shooting sparked anger among youths who claim to have suffered from police brutality and racism.
One of the rioters in Husby told Swedish Radio that racism was rampant where he lived, and that violence was his only way of being noticed.
"We burned cars, threw rocks at police, at police cars. But it's good, because now people know what Husby is... This is the only way to be heard," said the rioter, identified only by the pseudonym Kim.
In the suburb of Rinkeby, six cars parked alongside each other were torched Thursday night. A police station and several shops in another area Aelvsjoe were set on fire, but the flames were quickly extinguished.
