Bemused Swedes have been defending their record as a low-crime society in the wake of US President Donald Trump's speech in Florida last week in which he appeared to refer to a terrorist attack in Sweden that did not happen.

Trump later said he was talking about a Fox News programme highlighting allegedly surging crime statistics in Sweden and linking them to rising immigrant numbers, after a record 163,000 asylum-seekers arrived in 2015.

On Monday, he tweeted: "The FAKE NEWS media is trying to say that large scale immigration in Sweden is working out just beautifully. NOT!"

Swedes have leapt to their country's defence.

"Last year there were app 50 pct more murders only in Orlando/Orange in Florida, where Trump spoke the other day, than in all of Sweden. Bad," former prime minister Carl Bildt tweeted.

Few would argue with the fact that Trump's picture of Sweden is at odds with statistics.

Sweden ranked 187th out of 218 countries in 2014 in terms of murders per capita, according to a survey by United Nations Office on Drugs and Crime. The murder rate in the United States, which ranked about 110th, was more than four times higher.

The suggestion that the recent rise in asylum numbers has triggered a crime wave appears to have come from media reports rather than from statistics, as Swedish police do not register suspects' ethnic origins, only their gender and age.

"There is no basis for drawing the conclusion that crime rates are soaring in Sweden and that that is related to immigration," Stina Holmberg at the National Council for Crime Prevention said.

The most recent official survey from 2005 does show foreign-born Swedes are more than twice as likely to be suspects in criminal investigations, but their ethnicity is not the main reason for this.

"Minorities are often over-represented in criminal statistics, but when you adjust for socio-economic factors, that disappears almost completely," Social and Justice Minister Morgan Johansson said recently.

Sweden is nevertheless not the crime-free utopia that some might like to believe.

A surge in gang-related violence has pushed up the murder rate in the last couple of years.

In the southern city of Malmo, a town just shy of 300,000 people, 12 people were killed last year, according to local media. That was a record and gives it a murder rate per capita three times higher than that of London.

In 2013, in the mainly immigrant Stockholm suburb of Husby, around a hundred cars were burned and seven police were injured in five nights of rioting, which spread on a smaller scale to other cities across the country.

Emergency services are regularly attacked by stone-throwing youths and on Monday night, rioters in a suburb of the capital battled police and burned a handful of cars.

But the violence has clearly not spiralled out of control.

"There are no areas where the police don't go," police spokesperson Johanna Blomqvist said in an email in reply to Reuters questions.

And an annual survey of Swedes by the National Council for Crime Prevention shows crime rates broadly unchanged over the last 10 years.

Many Swedes do appear to be worried about immigration, however.

The anti-immigration Sweden Democrat party, which has called for a big rise in police numbers and tougher sentences for criminals, has surged in popularity and is now vying for second spot in polls.

Sweden took in more asylum-seekers relative to the size of its population than any other European Union member in 2015. In a backlash, many asylum centres have been targeted by far-right attackers and several have been burned to the ground.

Integrating the new arrivals is also likely to be problematic. Segregation, poor schools and unemployment blight the prospects of many young people, often those with immigrant backgrounds.

Unemployment among foreign-born Swedes is around 15 percent compared with 5 percent among those born in the country.

"Sweden, like many other countries, has many opportunities, but faces many challenges," Prime Minister Stefan Lofven said.

- Reuters