Facing a tsunami of disinformation about the treatment of Muslims that has in recent months fueled protests from Stockholm to Baghdad, Sweden decided it needed to fight back.

It turned to the Psychological Defense Agency, a part of the Ministry of Defense that its government created last year. The agency has become the first line of defense for a country facing a sustained information attack from abroad.

The country’s leaders are borrowing from an old Cold War strategy to steel the country’s 10 million people for the possibility of “total war” with the Soviet Union. Today’s main threat — though not the only one — is the Soviet Union’s successor state, Russia. According to the agency’s officials, the Kremlin has targeted Sweden with a concerted online campaign on social media and elsewhere to discredit the country and undermine its bid to join the NATO alliance.

After working quietly behind the scenes, the agency has now explicitly accused Russia of exploiting recent protests by immigrants and others in Sweden that have included burning copies of the Quran, an act of desecration that is deeply offensive to Muslims. The outrage has already had an impact: delaying Sweden’s accession to NATO because of objections by another member, Turkey.

“They were on a level that we’d never seen before,” Mikael Tofvesson, the agency’s director of operations, said in an interview, referring specifically to Russian efforts to amplify global reaction online to a protest outside Stockholm’s largest mosque on June 28.

Other countries have scrambled in recent years to counter foreign influence operations, including France, which has created a similar agency, but Sweden is now on the front lines of a fight over the country’s security, its social cohesion and even its democratic foundations. Russia’s invasion of Ukraine — and Sweden’s subsequent decision to seek NATO membership — have put the country in the Russian cross hairs.

The work of the Psychological Defense Agency could become a model for how democratic governments can fight back — or a symbol of how ineffective they are against determined authoritarian adversaries.

Sweden’s prime minister, Ulf Kristersson, who has led a coalition government since elections last fall, said that “states and statelike actors” were “actively exploiting” the protests in Sweden. In a statement with Denmark’s leader late last month, he said that Sweden faced “the most serious security situation since the Second World War.”

In Sweden, as elsewhere, the question of what to do in the face of an information onslaught has become increasingly fraught, pitting traditions of tolerance for free speech against the dangers that malicious information online poses.

In the United States, the debate has become increasingly partisan, with Republicans accusing the federal government of stifling critics at home. Last year, an effort to create a disinformation advisory board at the Department of Homeland Security was scuttled amid fierce opposition.

The Psychological Defense Agency also raised political concerns when it was proposed, but its leaders have emphasized that mandate allows it to address only foreign sources of disinformation, not content generated in Sweden.

The challenge is one facing all democracies that, as a matter of principle, decline to enforce official ideologies, allowing divergent points of view of what is true or false.

“The government can’t control the truth if it’s going to be a democracy,” said Hanna Linderstål, the founder of Earhart Business Protection Agency, a cybersecurity firm in Stockholm, and an adviser to the International Telecommunication Union, part of the United Nations.

The Psychological Defense Agency began operations in January 2022, but some of its functions previously fell to a civilian department in the Civil Contingencies Agency. Its roots extend further back, to 1953, when Sweden, though neutral, feared Soviet domination in the ideological struggle between the West and Communism.

The decision to revive the country’s capacity to combat information war came after Russia’s seizure of Crimea from Ukraine in 2014, beginning a military intervention that has been characterized by waves of disinformation. Officials in Sweden, as elsewhere, have expressed concern that the propaganda has succeeded in sowing confusion and doubt among European electorates, undermining government policies to counter Russia’s aggression.

“When it comes to information war,” said Pär Norén, a senior analyst who conducts training sessions for the agency, “it is the brain that is the battle space.”

From the agency’s inception, Sweden faced intensive disinformation campaigns. They began in late 2021 with posts on Twitter, YouTube and other social media platforms expressing anger over the plight of an Iraqi immigrant in Sweden whose children were removed from his custody by the country’s child protection services.

The accusations metastasized into false accusations that Sweden was kidnapping Muslim children and forcing them to eat pork or otherwise violate Islamic traditions, which spread online in Arabic-speaking countries, including Egypt, Morocco and Lebanon, as well as Turkey.

The immigrant was not, in fact, Muslim, but Mandaean Sabian, an adherent of an ancient monotheistic faith in southern Iraq that reveres John the Baptist, among other prophets.

The accusations have persisted online, including on a YouTube channel with nearly one million subscribers that first circulated them. One of Russia’s state television networks followed this year with a similar report involving an ethnically Russian immigrant family from Latvia, saying Sweden would not allow the children to speak Russian, which is not true.

The controversies over social services gave prominence to a new political party, Nyans, or Nuance, that has built support among the country’s immigrant voters. The party’s leader, Mikail Yüksel, acknowledged that the accusations of state kidnappings were false but nevertheless criticized the government for its policies.

“Sweden is an anti-Islamist country,” Mr. Yüksel, who emigrated from Turkey, said. “This is not disinformation. This is the truth.”

The government was slow to respond to the accusations about social services, but the new government under Mr. Kristersson announced a series of measures this year in response, including bringing on more staff members at the Psychological Defense Agency, which now has 55 employees.

The agency’s headquarters is in Karlstad and it has an office in Solna, a suburb of Stockholm. There, it occupies an inconspicuous yellow building on the campus of the Karolinska University Hospital, which has opened its doors for refugees and casualties from the war in Ukraine.

“What we see now is a full-blown, full-scale war in Europe,” said the agency’s director general, Magnus Hjort, a former historian who wrote a report proposing the reconstitution of a department devoted to psychological defense. “And Sweden is not neutral.”

According to the agency, Russian state media and online accounts have also amplified a series of protests that have featured the burnings of the Quran over the past two years — in Russian and in Arabic across the Middle East. Some of the sources, it found, were the same ones circulating false reports about kidnapping Muslim children. Other researchers have suggested that Russians were involved in helping to instigate the protests.

One of the first protests involved Rasmus Paludan, a far-right politician in Denmark who also has Swedish citizenship, who burned a copy of the Quran in Jönköping in 2002. He did it again in January in front of the Turkish Embassy in Stockholm, prompting outrage in Turkey that has helped stall approval of Sweden’s application to join NATO.

The cost of the permit for Mr. Paludan’s protest in January — 320 krona, or about $30 — was paid for by a Swedish journalist who had previously worked for Russian media, Chang Johannes Frick. Mr. Paludan, however, denied any association with Russia, saying in an email that he opposed Russia’s invasion and that he had staged the protest to draw attention to Turkey’s position.

“I wanted to send a signal to Erdogan that he should not interfere with freedom of expression in Sweden,” he wrote, referring to Turkey’s president, Recep Tayyip Erdogan.

Another protester, Salwan Momika, has held a series of small demonstrations desecrating the Quran, twice setting off demonstrations in Iraq that resulted in attacks on Sweden’s embassy in the capital, Baghdad. Mr. Momika, an Iraqi Christian who immigrated in 2017, initially agreed by email to answer questions about his motivations, but he did not respond when asked about his connections to Russia.

Mr. Hjort and other agency officials declined to detail the evidence of Russia’s involvement, and so far the agency has produced few public reports about foreign disinformation campaigns. Much of its work involves advising other government agencies behind the scenes to raise awareness of the threat of foreign interference. That included training sessions for municipal departments handling child welfare cases among immigrants. It did conduct a public service campaign — in Swedish, Arabic and English — ahead of last fall’s elections that used humorous posters to warn of the falsehoods lurking online.

Mr. Hjort said that the agency was regularly in touch with the social media platforms but that it did not ask for the removal of accounts. Only once has it publicly called out a source of disinformation — Shoun Islamiya, the YouTube channel in Egypt that brought international attention to the false accusation of kidnapping children — but it remains online.

“The best way to protect a society against disinformation, if you live in a democratic society, is to increase awareness about the threats and your own vulnerabilities among the population, so they make the right decision,” said Mr. Tofvesson, the director of operations. “And that is the Swedish way.”