The United States Friday sent an email to all U.S. nationals living in Sweden, warning them to stay away from the affected areas, The Local.se reported.
"Even demonstrations intended to be peaceful can turn confrontational and possibly escalate into violence," the email said. "We recommend that U.S. citizens avoid the areas where such demonstrations are occurring if possible, and, as always, exercise caution in the vicinity of any parades or protests."
The U.K. Foreign Office also warned citizens traveling in Sweden, saying, "You should avoid large gatherings, take care and monitor local news reports."
"There have been riots in the suburbs of Stockholm every night since 19 May. Suburbs affected so far are Husby, Hagsatra, Ragsved, Skogas," the Foreign Office said on its website.
Meanwhile, 11 cars and parts of two schools and a police station were charred early Friday after a fifth night of unrest in immigrant enclaves around Sweden's capital.
Some 300 to 500 youths gathered around eight blazing cars in northwestern suburban Rinkeby, with some young men vandalizing other vehicles, police told the Swedish news agency TT.
More than a dozen agitators went into a subway station, breaking train windows and threatening transit workers, Swedish newspaper Expressen reported.
In nearby Tensta, a firebomb was thrown into a school, Britain's ITV News reported. The fire was put out. Firefighters were later called to another blaze in a kindergarten school in Kista.
At least three more cars were set afire in the southwestern Norsborg suburb and a police station in south-suburban Aelvsjoe was scorched after young men set part of it on fire, authorities said.
At least eight people were arrested, police told TT.
No serious injuries were immediately reported.
Police and news accounts characterized the fifth night as calmer than the night before.
Prime Minister Fredrik Reinfeldt had called for calm, saying violence and arson were not freedom of speech but "hooliganism."
The violence, which spread to more than 15 suburbs, started Sunday in north-suburban Husby -- near where some of Thursday night's violence occurred -- after a police standoff led to the fatal police shooting of a 69-year-old man in his apartment hours after the man wielded a machete in public.
Police said they'd tried in vain to mediate with the holed-up man and justified the killing as self-defense.
Critics charged gross police misconduct, which they alleged was typical of police treatment of immigrants.
Selcuk Ceken, a youth center worker in one of the affected suburbs, told Britain's Sky News it was hard to know precisely why the youths were rioting, but he gave several possible reasons.
"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," Ceken said.
Swedish newspaper Aftonbladet called the violence a "gigantic failure" of government policies, which it said in an editorial had led to inner-city ghettos.