The leader of a far-right party with roots in the neo-Nazi movement says it has “won” Sweden’s national election, after preliminary results showed it secured more than a sixth of the vote.

After a campaign dominated by debates over immigration, 17.6 per cent of the electorate opted for anti-immigrant party the Sweden Democrats, up from 12.9 per cent in the last election.

Voters simultaneously handed Sweden’s ruling Social Democratic Party its worst-ever election result – 28.4 per cent as the count neared completion – though that was still enough to leave it the single largest party in the Riksdag, Sweden’s parliament.

The ruling Social Democrats, Greens and Left Party coalition won 40.6 per cent of the votes while the opposition bloc made of the Moderates, the Christian Democrats and the Centre Party and the Liberals won 40.3 per cent of the votes.

The potential for an immigration backlash resulting in a big boost for the Sweden Democrats inspired fear among many Swedes before the election. But despite the rise in support, its showing was not as strong as many polls predicted, though still enough to secure a third-place finish.

Ulf Kristersson, leader of the centre-right Moderate Party that came in second, called on prime minister Stefan Lofven to resign, and claimed the right to form Sweden’s next government.

But Mr Lofven, who brought the Social Democrats to power in 2014, said he intended to remain in the job. Sounding sombre, he told his supporters the election presented “a situation that all responsible parties must deal with”, adding that “a party with roots in Nazism” would “never ever offer anything responsible, but hatred”.

He said: “We have a moral responsibility. We must gather all good forces. We won’t mourn, we will organise ourselves.”

Final election returns were expected later in the week. Turnout in the election was reported at 84.4 per cent, up from 83 per cent in 2014.

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The elections are far from over however, as there will be a drawn out period of negotiations between the centre-left and centre-right blocs requiring cross bloc alliances to be formed, or a joining of forces with the insurgent Sweden Democrats, a move which is unpopular with most parties.

The preliminary results made it unlikely any party would secure a majority of 175 seats in the 349-seat Riksdag. It could take weeks or months of coalition talks before the next government is formed.

Both the left-leaning bloc led by the Social Democrats and the centre-right bloc in which the Moderates is largest of four parties have said they would refuse to consider the Sweden Democrats as a coalition partner.

Sweden – home to the Nobel prizes and militarily neutral for the better part of two centuries – has been known for its comparatively open doors to migrants and refugees.

Sunday’s general election was the first since the country of 10 million took in a record 163,000 refugees in 2015 as mass migration to Europe rose dramatically.

Mr Lofven eventually said Sweden could no longer cope with the influx and immigration laws were tightened.

Party Number of seats Number of seats in previous election Social Democrats 101 113 Green Party 15 25 Left Party 28 21 Centre-left bloc 144 159 Moderates 70 84 Centre Party 31 22 Liberals 19 19 Christian Democrats 23 16 Centre-right bloc 143 143 Sweden Democrats 62 49

Like other far-right parties in Europe, the Sweden Democrats, which first entered parliament in 2010, has strived to mend its public image in recent years in a bid to garner more supporters.

Sweden Democrats leader, Jimmie Åkesson, has claimed there is no place for racism in the party and has expelled some members for expressing pro-Nazi views. He has also changed the old party symbol, a flaming torch, into a softer looking blue and yellow flower.

He has also, however, infamously called Sweden’s growing Muslim population “the biggest foreign threat since the Second World War”.

His party presented the vote on Sunday as a ballot on hot button issues including immigration and Sweden’s famous welfare system.

The party made its first mark in politics by gaining municipal council seats in 2006, and since then slowly helped revise long-accepted social norms for what Swedes could say openly about foreigners and integration without being considered racist.

At a post-election rally, Mr Åkesson said the party’s improvement on the 12.9 per cent it scored in 2014 represented victory.

“No one can take that away from us,” he said. “We will have an immense influence over what happens in Sweden in the coming weeks, months, years.”

He also criticised Mr Lofven’s government for “prioritising” the needs of new immigrants over the ones of Swedish citizens.

“We won,” he said as he declared the estimated 14 parliament seats the Sweden Democrats picked up a victory other parties could not ignore in coalition negotiations.

“This party has increased and made the biggest gains. Everything is about us,” Mr Åkesson said. “I am ready to talk with others.”

Although Sweden has long been lauded as a bastion of liberal values, fears of straining its generous welfare system prompted a wave of anti-immigrant sentiment in recent years

In May, the government announced plans to cut, almost by half, the number of refugees and migrants entering the country.

This may mean some kind of accommodation of the Sweden Democrats may be likely – if not now, then some time in the future.

Many therefore believe the Moderate Party leader, Mr Kristersson will seek to form a minority centre-right administration with ad hoc parliamentary support from the Sweden Democrats and possibly an official alliance with the Christian Democrats.

What any agreement could look like remains to be seen and according to Nicholas Aylott professor of political science at Södertörn university could result in “a rather extreme form of minority government – one whose only party has attained just a quarter or even a tenth of the seats in parliament.”

And though this situation has been brought about by the rise of the Sweden democrats and other parties struggles on how to manage their presence in parliament, some observers say that the patterns of voting this election does not necessarily indicate the rise of the right wing.

”The aggregate movement of voters does not say everything about the way in which voters have shifted parties from the previous election to today. The losses of the social democrats are not necessarily the gains of the radical right.” Professor Sarah De Lange, from the University of Amsterdam, who specialise in populist and radical movements. “More striking than the gains and losses of individual parties is the further fragmentation of the party system. The bigger parties are getting smaller and the smaller parties getting bigger.”

“Instead, the voters that have deserted the social democrats and the mainstream right are likely to have left to a variety of parties for a variety of reasons,” Ms De Lange added

Others believe if a shift does not occur in Swedish politics then the Sweden Democrats are likely to continue to make larger gains similar to other far right parties across Europe.

“If things carry on as they are going, it will happen,” said Ann-Cathrine Jungar, a far-right specialist at Södertörn University. “In Denmark, Norway, Austria, the far right is now accepted by the centre right. I can see that here one day.”