The stories are doom-laden, laced with vitriolic sneers about Emmanuel Macron, Volodymyr Zelenskiy and Ursula von der Leyen. Ukrainians are “ready to depose” their leader, Macron is breaking French “rules” with aid to Ukraine, an “uncontrolled influx” from the east is “seriously harming the Germans”.

According to new research, these are just a few examples of a vast pro-Russian propaganda campaign washing over Facebook accounts of French and German citizens, before the European parliament elections next month.

The adverts – collected by tech expert Paul Bouchaud and shared with the Observer – all ran on Facebook during the first 13 days of May. None were labelled as political advertising, according to Bouchaud, who sees that as a clear breach of Meta’s rules and a possible breach of EU law. In April, the EU executive opened an investigation into Meta over suspicions that it was failing to prevent the dissemination of deceptive ads and disinformation.

Bouchaud, a PhD researcher at the School for Advanced Studies in the Social Sciences in Paris, thinks that the ads reveal a “systemic failure” at Meta. In an earlier report for AI Forensics, Bouchaud found that the pro-Russian propaganda ads had reached 38m individual accounts in France and Germany between August 2023 and March 2024, with most going undetected. Fewer than 5% of undeclared political ads shown on Facebook in 16 European countries were caught by Meta’s detection system, according to AI Forensics.

“It is technically feasible to detect in real time a coordinated propaganda network,” Bouchaud said. “The fact that Meta does not systematically address this issue [shows] a lack of willingness, more than a lack of technical feasibility.”

Meta said it welcomed research into “inauthentic activity” using its ad library, but rejected the claim that no action had been taken. “While the full findings [on the May ads] weren’t shared with us, a sample of these ads clearly shows that our security team had already blocked them and disabled the pages behind these ads, as part of our routine, daily enforcements against inauthentic behaviour.”

Meta had similarly rejected the claims in AI Forensics’ earlier report, saying the pages cited were removed within hours. “This is a highly adversarial space with malicious groups constantly evolving their tactics to evade detection by companies across the internet, which is why we invest heavily in regularly sharing our threat research publicly,” Meta said.

Disinformation is just one facet of foreign interference that European democracies are confronting, alongside spying, influence operations and cyber-attacks. “The scale [of the threat] is very high,” Nathalie Loiseau, a French MEP in Macron’s party, who chairs the European parliament’s subcommittee on security and defence, told the Observer.

“Russia has been investing for decades in interference in a certain number of western countries, notably France,” Loiseau said, referring to Kremlin support for French political parties, close links with French intellectuals and politicians, and Russia’s “massive” investment in information manipulation.

Nor is it an abstract threat. “It is not science fiction, it is already here,” Loiseau said, citing the 2023 Slovak elections, where a pro-European, pro-Nato candidate, Michal Šimečka of Progressive Slovakia, lost a tight race to Robert Fico, the populist leader who was the victim of an assassination attempt this week that shocked Europe. Šimečka’s defeat came after a fake audio emerged purporting to show him discussing how to rig an election by buying votes.

Katarína Klingová, a senior research fellow at the Globsec thinktank based in Bratislava, cautioned that “we really do not know” how that fake influenced the result, but said it played into well-established narratives. A poll by Globsec in March 2023 found that 53% of Slovak citizens expected the election to be rigged. “So this really confirmed that [narrative] and the people who are more vulnerable to pro-Kremlin propaganda believed it.”

European officials have uncovered thousands of examples of disinformation in nearly a decade, and they are braced for a surge of malign stories in the final days before the votes, designed to sow doubt and confusion about the democratic process. In recent elections across the continent, voters have been confronted with made-up stories about electoral pens with disappearing ink, fake polls and fraud via voting machines, mailing or online voting.

Ursula von der Leyen, who is campaigning for a second term as European Commission president after the EU elections, last week promised to create an EU centre to counter foreign interference, if re-elected. “Europe now needs its own dedicated structure on countering foreign interference,” von der Leyen told a democracy conference in Copenhagen. The commission, she added, would be “vigilant and uncompromising” in the enforcement of EU law, notably the EU’s Digital Services Act, which is intended to protect people against disinformation – and provides the legal basis for the investigation into disinformation on Meta platforms.

Loiseau said she took a “very favourable” view of an EU centre to counter foreign interference. She has argued that the EU needs an equivalent to France’s Viginum agency, which helped expose the doppelganger operation, a relentless campaign that created clone versions of official and media websites, including France’s foreign ministry, Le Monde, the Guardian and Bild, to peddle pro-Kremlin narratives.

In an interview before Von der Leyen’s pledge was announced, Loiseau said the EU’s response was inadequate to the scale of the threat: “There is a kind of indolence or complacency that allows Russia to keep on working”. In 2023 MEPs voted in favour of a resolution to strengthen the EU’s response to disinformation, including naming countries thought to be engaged in such dark crafts. “Russia profits from silence,” Loiseau said. “There is nothing worse for those who commit interference than the light.”