Sweden is not exactly synonymous with feisty politics, but that looks set to change after a populist anti-immigration party surged into position as the country’s second-largest political force in a weekend election dominated by fears of gang violence that has made some areas of the Nordic country among Europe’s most dangerous.

Overall, a conservative opposition bloc including the anti-immigration party, the Sweden Democrats, had an extremely narrow lead over the incumbent center-left bloc with 94 percent of the votes counted.

Analysts expected that the final tally would confirm a conservative win, but the election was so close that electoral officials said they would not have the final result until outstanding mail-in votes and votes from abroad are counted later in the week.

It was a suspenseful election to the end, with polling ahead of the vote showing the race too close to call and exit polls published Sunday night initially predicting a center-left victory. As the official results came in over the following hours, the center-left’s edge slipped away.

One certainty, however, is that the result marked a success for the Sweden Democrats, which won its best result since entering parliament in 2010.

The party’s founders in the 1980s had links to fascist and neo-Nazi movements, but over the past two decades it has worked to move to the mainstream under its 43-year-old leader, Jimmie Akesson. Its transformation included changing its official logo to a flower from a torch and expelling the most radical members.

Supporters like the party’s tough vows to crack down on crime and place strict limits on immigration, while opponents fear that its historic roots make it a threat to Sweden’s democratic identity.

The Sweden Democrats, which according to preliminary figures won 20.6 percent support, up from 17.5 percent four years ago, gained on the rising fears of crime in largely immigrant neighborhoods and a perception that the center-left leaders failed on that front in its eight years in power.

This year so far there have been 273 shootings, 47 of which were deadly, according to police statistics. Those shootings also resulted in 74 people being injured.

The left bloc is headed by Prime Minister Andersson, Sweden’s first female premier.

Ms. Andersson’s Social Democrats, who have been in power in Sweden since 2014, remain the largest party, even gaining slightly to take 30.5 percent of the vote according to the incomplete results. Ms. Andersson said Sunday night that it was obvious that the social democratic movement, which is based on ideals of creating an equal society and a strong welfare state, remains strong in Sweden.

With eight parties contending for seats in the 349-member Riksdag, Sweden’s parliament, none can secure a majority of 175 seats, meaning that laws can only be passed with different parties working together.

The not-yet-final count indicated that the conservatives would have 176 seats and the center-left would have 173.

“It is extremely close. Things can change, but I doubt it,” a sociologist at Stockholm University, Zeth Isaksson, said. “As it is now, it is more likely that the right side will win.”

The Sweden Democrats wants to be part of a government, but this is unlikely to happen because there are parties in the center-right bloc that oppose it, Mr. Isaksson said.

The Sweden Democrats’ party secretary, Richard Jomshof, said Monday: “It is clear that we must be able to discuss ministerial posts. It is clear that we must be able to talk about the position of prime minister, speaker of parliament, and the presidium positions in the various Riksdag committees.”

A senior member of the center-right Liberals told Swedish radio Monday morning that it cannot allow the Sweden Democrats to be part of a government. Also on Monday, Mr Akesson told party members, “Right now it looks like there will be a change of power.”

If the right prevails, the Sweden Democrats will have “very strong leverage” and will push for some of its issues, like tightening immigration laws, Mr. Isaksson said. Either way, Sweden is likely to face a lengthy process to form a government, as it did after the 2018 election.

Ms. Andersson, a 55-year-old economist, became Sweden’s first female prime minister less than a year ago and led Sweden’s historic bid to join NATO following Russia’s invasion of Ukraine in February.