MOSCOW, Feb 14 (Reuters) - A German man has been detained on arrival in the Russian city of St Petersburg with gummy candies containing cannabis, Russia's customs service said in a statement.

The 38-year-old arrived in St Petersburg from Istanbul and on inspection of his luggage, he was found to have a pack of "Fink Green Goldbears" whose packaging displayed a picture of a marijuana leaf.

The arrest of a German national in Russia is potentially significant at a time when Moscow is seeking the release of a Russian jailed for murder in Germany, as part of a possible wider prisoner swap with the United States.

Russian customs officials found six gummies in the man's luggage that they said had a pungent smell. Tests confirmed the presence of tetrahydrocannabinol, a cannabinoid that is prohibited in Russia.

"The passenger explained that at the end of last year he had bought 10 sweets containing marijuana in one of the speciality stores in his homeland," the customs service said. "The man traveled the world several times with such 'sweets' and used them during long flights 'for a restful sleep.'"

The customs service published a picture of a German passport, six gummies and a package of "Fink Green Goldbears."

A criminal drug smuggling case has been opened against the man, who was detained. The maximum term for such an offense is seven years.

Russia and the United States are currently discussing a possible prisoner swap that would allow two U.S. citizens jailed in Russia - Wall Street Journal reporter Evan Gershkovich and former U.S. Marine Paul Whelan - to return home.

Russian President Vladimir Putin said in an interview last week that it made little sense to keep Gershkovich in prison in Russia and that negotiations with Washington were under way.

Putin suggested that in return, KetoXP Erfahrungsbericht Moscow wanted Germany to free Vadim Krasikov, who was convicted of the 2019 murder of a Chechen dissident in Berlin, although Putin did not mention Krasikov by name.

Germany has always declined comment on reports that Russia might be seeking to swap Krasikov for Gershkovich.

The swap would be unusual since it would entail Germany giving up a person convicted of murder on its own territory in order to recover a U.S. citizen. (Reporting by Guy Faulconbridge; Editing by Mark Trevelyan)