DAVOS, Switzerland (Reuters) - Swiss officials foiled an apparent spying operation by Russians posing as plumbers in Davos, site of the World Economic Forum's annual meeting, a newspaper reported on Tuesday, but police did not confirm key details of the account.

The report in the Tages-Anzeiger newspaper said the two Russians were checked by Swiss police in August last year in the ski resort, which is hosting the WEF gathering of the global business and political elite this week. The pair presented diplomatic passports and left the country, the paper said.

Police in the eastern Swiss canton of Grisons said two men with Russian diplomatic passports had been the subjects of a routine identity check in Davos in August 2019, but no connection had been established between their visit and the WEF.

"It is true that we checked two Russian citizens in Davos and they identified themselves with diplomatic passports, but we could not ascertain any reason to detain them. They were allowed to go," a cantonal police spokeswoman said, adding police had never identified the men as plumbers.

A spokesman for the Russian embassy in Bern dismissed the report, saying two Russian diplomats accredited outside Switzerland had been checked and allowed to go on their way.

"Diplomatic passports are given to high-ranking officials, not to manual laborers," he said. "I think this was probably a dumb joke."

Maria Zakharova, a spokeswoman for the Russian Foreign Ministry in Moscow, said she was not aware of the incident.

Investment fund manager Bill Browder, who has led a campaign to expose corruption and punish Russian officials whom 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.

"The Russians are actively targeting all of their enemies in all different countries - they have huge resources and Davos is an important place, and this is the one place I can come and personally challenge Russian officials over the murder of Sergei Magnitsky," Browder told Reuters Today in Davos on Tuesday.

Russian prosecutors have said they suspect Browder of ordering a string of murders, including of Magnitsky, in a twist the financier has dismissed as ludicrous.

(Reporting by Kathryn Lurie in Davos and Michael Shields in Zurich; Editing by Alex Richardson)