Held annually in the Swiss ski resort of Davos, the WEF gathers world leaders such as U.S. President Donald Trump and German Chancellor Angela Merkel with thousands of figures in business, NGOs, academia and more.

Two Russians who identified themselves as plumbers despite carrying diplomatic passports were checked in Switzerland on suspicion of espionage ahead of this week’s World Economic Forum (WEF), the Tagez Anzeiger newspaper reported Monday.

The two unnamed men were taken in for a routine identity check in August 2019 after authorities learned that they were both staying in the country for the same three-week period, Tagez Anzeiger reported, citing the police spokeswoman in the canton of Graubünden where Davos is located.

It was “obvious” that the two men had their sights on the WEF and the high-profile figures who attend the forum, Tagez Anzeiger cited unnamed sources familiar with the case as saying. They could have been working to establish a long-term audio surveillance or hacking program, the sources said.

While both men carried Russian diplomatic passports, they identified themselves as plumbers, Tagez Anzeiger reported. Neither of the men were accredited as diplomats in Switzerland, the police said, and as a result were unable to claim diplomatic immunity after being detained.

The Russians claimed immunity, however, and Russian state representatives threatened diplomatic consequences if the men were arrested. Ultimately, police released the men and allowed them to leave the country with no subsequent entry bans.

“There were no indications of criminal acts during the check," the Graubünden cantonal police spokeswoman told the newspaper. She later told Reuters that police had never identified the men as plumbers, contradicting the account in Tagez Anzeiger's report.

The Russian Embassy in Bern’s press secretary denied the espionage claims, telling Tagez Anzeiger that the men had been in Davos to help prepare for an event hosted by the state-run Roscongress Foundation during the WEF.

“There are people outside of the Russian Foreign Ministry who are given diplomatic passports,” the embassy was quoted as saying.

U.S.-British investor Bill Browder, who has led a campaign to expose corruption and punish Russian officials he blames for the death of his lawyer, Sergei Magnitsky, who died in a Moscow prison in 2009 after complaining of mistreatment, said the alleged incident showed the reach of the Russian state.