Stockholm (AFP) - Masked men chased migrants in Stockholm this weekend in a rare act of overt violence against refugees, but one that reflects smouldering tensions in Sweden as it grapples with the consequences of a record influx of migrants.

The attack came just days after a teenaged asylum-seeker killed a young woman working at an asylum residence.

Between 50 and 100 masked and hooded men chased and reportedly beat up "people of foreign appearance" on Friday evening at the Sergels Torg plaza in the heart of the city and handed out leaflets calling for "the street children of North Africa to get the punishment they deserve".

Police swiftly chased off the assailants, but footage of the racist attack shocked many Swedes as they struggle with conflicting emotions regarding the flood of arrivals.

On the one hand there is a deep-rooted, longstanding sense of humanity and willingness to give refuge to those in need.

While on the other, there is a grim realisation that the country's infrastructure is overwhelmed after welcoming more migrants per capita than any other European Union country in 2015.

"What is going on in Sweden?" asked daily Expressen on Sunday, listing a growing number of issues linked to migrants, including arson attacks on asylum residency centres and cultural as well as religious tensions.

On both the left and right wings, the Swedish media have squarely placed the blame on Prime Minister Stefan Lofven -- a Social Democrat whose party has hit record lows in the polls -- accusing him of downplaying the challenges facing the country.

"Those who dared discuss the link between the number of (migrant) arrivals and the capacity to welcome and integrate them were accused of painting a pessimistic picture and playing into the hands of the far-right," the centre-right daily Svenska Dagbladet wrote last autumn.

- 'Never thought this was possible' -

But in an editorial on January 26, the newspaper called for migrants who commit crimes to be expelled -- a proposal published the day after the fatal stabbing of Alexandra Mezher, a 22-year-old asylum centre social worker.

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Mezher, of Lebanese origin, was knifed by a 15-year-old boy as she tried to break up a fight in a centre for unaccompanied minors where she worked in Molndal, a suburb of Gothenburg in southwestern Sweden.

"We would never have thought this was possible in Sweden. We hold the government and the prime minister responsible," the victim's uncle told AFP.

Lofven responded quickly, visiting the scene hours after the killing, but his reaction stunned commentators.

"There's no easy solution," the prime minister said, prompting Sweden's paper of reference Dagens Nyheter to conclude: "Lofven has nothing to say."

A few days later the government announced it wanted to improve its efficiency at deporting asylum seekers whose applications are rejected, estimating that at least 60,000 of the 163,000 who applied in 2015 would be rejected and expelled.

In 2014 and 2015, Sweden, where 20 percent of the population has foreign origin, took in 245,000 asylum seekers, more than any other EU country per capita.

- Dilapidated 'Swedish model' -

The influx has dwindled to a trickle since Sweden reinstated border checks in November, but the large number of migrants has pushed the country's famed "Swedish model" -- a cradle-to-grave welfare state already a little worse-for-wear -- to the edge.

Sweden faces acute housing shortages and skyrocketing real estate prices, salaries so low for teachers and nurses that there are employee shortages, a lack of nursing homes, and, in a country that prides itself as an egalitarian society, the fastest growing inequality gap in the OECD.

Burdened further by the migration crisis, the degradation of the welfare state has left some Swedes with a sense of "paradise lost", fuelling the frustrations of society's weakest members.

"The country has changed a lot. It used to be a quiet place but now all you hear about is violence and attacks," Eva, a pensioner from the town of Boras where Alexandra Mezher lived, told AFP.

Obsessed by the "image Sweden has of itself as a big moral power" on the international scene, "the left has (over the years) forgotten Sweden's domestic needs and has as a result left the door wide open for the Sweden Democrats", the far-right party represented in parliament, historian Lars Tragardh told AFP.

The party has officially distanced itself from the racist and violent neo-Nazi movements that were active during the 1990s when Sweden opened its doors to refugees from the Balkans war.

Authorities now fear a resurgence of those groups.

Intelligence service Sapo suspects them of recruiting members among football hooligans, as appears to have been the case in Friday's migrant attacks.

Internet site Nordfront, run by the neo-Nazi movement SMR, confirmed that around "a hundred hooligans" from the AIK and Djurgarden clubs were involved in the attacks.

At an anti-migrant demonstration in Stockholm attended by around 200 people, several protesters were also seen wearing team colours.