A new wave of execution-style shootings in Sweden's third largest city has left police puzzled, raising concerns that Malmo has become a magnet for gang-related killings.

On Thursday dozens of police took to the streets in the southern Swedish city of 250,000 to try calm the public and to collect tips about the attacks, which come only a year after a suspected serial shooter was arrested there.

"We've never experienced anything like this before. It's exceptional that there have been so many murders in such a short period of time," police spokesman Lars-Hakan Lindholm said. "People are worried of course and want to talk about it."

In less than six weeks, five people have been shot dead in execution-style killings, prompting local police to ask for back-up from national investigators and for Malmo Mayor Ilmar Reepalu to call on the country's justice minister to implement tougher gun laws.

Sweden's gun control laws are fairly strict. Penalties for possessing illegal arms typically involve fines or up to one year in prison, but serious breaches of the law can result in a four-year sentence.

Lindholm said that due to the fast escalating death-toll police presence has now been bumped up by about 30 extra officers in the city on weekdays and by around 40 on the weekends. Malmo is an eclectic city, where about 40 percent of its residents are first- or second-generation immigrants.

The latest murder occurred on Tuesday, when a man in his late 40's was shot dead in broad daylight on an open street near his Malmo home.

Two days earlier, a 15-year-old boy was killed in the midst of the Malmo New Year celebrations.

"They're almost like executions," Lindholm said of the killings, but noted that there are still no suspects in the slayings and police remain baffled to what the motives might be.

The killings have upset many Malmo inhabitants who, just last year, saw the end of a near seven-year shooting terror by a lone gunman that targeted immigrants.

That suspect, 39-year old Peter Mangs, is currently facing charges for allegedly killing three people and attempting to murder another 13 victims in a series of sniper-like attacks.

Police say they see few links between Mangs and the latest shootings however, having largely ruled out that they're dealing with a copycat.

Instead, they indicate the incidents could possibly be gang-related, as the victims seem to have been carefully picked out.

"There is nothing pointing to that these are random shooting acts. There have been specific targets and the targets have been hit," Superintendent Borje Sjoholm told reporters at a news conference earlier this week.

"There are some common denominators between the five murders," he added.

In the light of the shootings, demonstrators will stage a protest against organized crime and illegal arms in Malmo on Friday. Some 4,800 people have so far signed up for participation.