A growing battle between the Hells Angels motorcycle club and ethnic minority gangs in Denmark and Sweden is prompting renewed concern that long-simmering gang tensions are intensifying amid economic woes and resentment over immigration.

The Danish capital of Copenhagen saw almost 60 gang-related shooting incidents in the past year, many of them in Nørrebro, just north of the city center. In March, a series of drive-by shootings and assassinations resulted in the deaths of three bystanders and sent shock waves through the city.

Efforts are now under way to boost the crime-fighting abilities of police, as well as address the causes that lead young people into gangs. Recent killings in Nørrebro prompted hundreds of residents to stage an antigang march.

"The violence has really shaken people, and they are wondering when there will be another shooting," says Kim Christensen, chairman of the Nørrebro district council, who led the march. It snaked through traditional turf of the Hells Angels before finishing less than a mile away, near the biker gang's main clubhouse.

"We're not used to this kind of trouble," says Ane Nissen, a student. "Normally, Copenhagen is very quiet and very safe. That's why we need to react now."

Danish police blame the recent surge in gang violence on an attempt by Hells Angels to get the upper hand over gangs consisting of first- and second-generation refugees.

"Hells Angels have been under pressure for a while now," explains Kim Kliver, head of the investigative division of Denmark's national police. "About two years ago, they realized that they were getting old and needed to recruit younger, more ruthless people."

In less than a year, the gang has doubled in size and created a "supporters club" called AK81, made up mainly of ex-convicts with a record for extreme violence. Police believe that victims of recent killings were chosen because they appeared foreign.

"There have always been social problems in this area, but now it's more divided," says Bendt Erik Krøyer, who runs a cultural center in Copenhagen's Blågårds Plads, a cobbled square dominated by social housing for refugees, mainly from the Middle East, and home to one of the warring factions.

This is not the first gang war in the region. The so-called "Nordic Biker War" in the mid-1990s pitted Hells Angels against the Bandidos motorcycle club. It resulted in a dozen murders and almost 80 shootings before a truce was proclaimed.

Danish police reacted to the first biker war by closing gangs' clubhouses and seizing finances. Today, the job is harder: There are at least a half-dozen ongoing gang feuds, and the gangs are harder to identify. A bridge that spans the narrow strait separating Copenhagen from the Swedish city of Malmö is also making it easier for gangs to evade authorities, Mr. Kliver says.

"The fact that the gangs operate in both countries is no barrier," he says. "We carry out 'Al Capone' operations on both sides of the border and look into how they are buying the cars and where they get their money. If they can't prove they earned it legitimately, we seize it."

Swedish police began recruiting specialists last month for a 200-person antigang squad, which some call "Sweden's FBI." Pressure has mounted for a tougher response following the 2001 bombing of a public prosecutor's home by a biker gang.

An estimated 50 criminal gangs, including the Bandidos and Hells Angels, as well as home-grown outfits with colorful names like Wolfpack Brotherhood and Werewolf Legion, compete for control of Sweden's narcotics, prostitution, and extortion rackets. According to official figures, extortion rackets have more than doubled over the past six years and grew by 50 percent in 2008.

Erik Lannerbäck, a former Bandidos member and youth counselor who now campaigns for gang prevention, says the recession may swell the ranks of Scandinavia's criminal gangs and lead to more turf wars. "With fewer job opportunities and the temptation of easy money," he says, "a lot of young guys will get drawn in."

Lasse Wierup, a crime reporter at Sweden's Dagens Nyheter newspaper, says that Swedish biker gangs have lost ground in recent years, often to competition from "immigrant gangs" from suburban projects.

"Hells Angels and Bandidos found it easy to get established in Sweden and Denmark because they had no organized enemies and could just walk in and take over," he says. "The biker gangs were founded on a myth that they were extremely dangerous and could get you wherever you are. That works on ordinary people – but not on the new generation of armed criminal gangs."

Sweden's justice minister, Beatrice Ask, recently said there was a need to "react very forcefully" to the threat, while her Danish counterpart, Brian Mikkelsen, announced "extraordinary steps," including doubling jail sentences for gang-related offenses.

Some activists, though, say that more should be done to prevent youths from joining gangs in the first place. Khosrow Bayat runs a crime-prevention program that provides extra tuition, sports activities, counseling, and part-time jobs for young people in one of the worst-affected projects in Nørrebro.

"The most vulnerable kids are boys in their early teens. They see gang members going around with cool clothes and girlfriends, and it affects them," Mr. Bayat says. "If you give them an opportunity early on to succeed in the mainstream, then you can close off the route to the gangs....

"We need to give them something more interesting to do," he adds, "than be lookouts for street gangs."