Officials from the Graubünden cantonal police department told the Financial Times that officials believe two Russians stopped in Davos in August 2019 were part of a ring of spies sent by the Kremlin to spy on the World Economic Forum.

Police suspected that the men were posing as plumbers to install recording devices around Davos to monitor conversations between leaders during the annual forum, taking place this week.

The men, who had diplomatic passports, were stopped at a high-end ski resort in August 2019.

Police did a routine identity check on the men after they were alerted of the pair's lengthy stay, but they found no criminal activity going on at the time.

It remains unclear why officials believe the men were spies.

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Police in Switzerland foiled an apparent spy plot by a group of Russians who were posing as plumbers in Davos, the site of the annual World Economic Forum, according to a report from the Financial Times and a local Swiss paper.

Officials from the Graubünden cantonal police department told the Financial Times that authorities found two men with Russian diplomatic passports during a routine identity check in August 2019, after they were alerted of the pair's lengthy stay at a high-end ski resort.

At the time, the men weren't identified as plumbers, and police found no criminal activity going on. The men said they had diplomatic protections, but officials found no connection between their visit and the upcoming forum, which is taking place this week.

After having their passports checked by officials, the two men left the country, according to Reuters.

Zürich's Tages-Anzeiger newspaper reported that police now suspect that the men were actually Russian intelligence agents employed by the Kremlin to spy on officials during World Economic Forum. The officials reportedly suspected that the men were the start of a larger spy ring posing as tradesmen to install recording devices around Davos.

It remains unclear what led the police to believe the men were spies.

A representative for the Russian embassy in Switzerland, Stanislav Smirnov, told CNBC that the reported suspicion of Russian diplomats was "one more attempt to undermine Swiss-Russian relations."

"The story goes, as far as I understand it, is that police wanted to check documents of men who they thought were suspicious. They were released, but still observed. The police did not see anything suspicious and the men just left," Smirnov told CNBC.

A spokesman for the Russian embassy in Bern told Reuters that diplomatic passports are only handed out to high-ranking officials, and manual laborers would not have such documents.

"I think this was probably a dumb joke," he said.