Russia's state-run news agency says the country's security agency, the Federal Security Service, has detained and charged a former staff member of the US consulate general in the far eastern city of Vladivostok with secretly cooperating with a foreign country.

TASS reported on Monday that if found guilty, the former staffer could face up to eight years in prison.

The nationality of the accused man has not been disclosed. But local media reports say he is in his 60s and worked for the consulate general for more than 20 years. He was reportedly detained near his home in Vladivostok in March.

Russian Deputy Foreign Minister Sergey Ryabkov told reporters on Tuesday that it is obvious certain unacceptable activities of hostile countries are increasing.

He said the detention and prosecution of the man is "proof" of that.

US State Department Principal Deputy Spokesperson Vedant Patel told a press briefing on Monday that he has seen those reports, but doesn't have anything additional to offer at this time.

In March, Evan Gershkovich, an American reporter for The Wall Street Journal, was detained by Russia's security service on suspicion of espionage. The US government has urged his release, but the Russian side rejected the request.