Russia's TASS news agency reported Monday that South Korean citizen Baek Won-soon has been held in the Lefortovo detention facility in Moscow since late February, and a court extended his detention until June 15, citing a law enforcement official, Yonhap news agency reported.

Baek was arrested by Russian law enforcement earlier this year in the Russian Far East city of Vladivostok and transferred to Moscow for further investigation, according to the news report.

TASS cited a law enforcement source as saying that Baek was handing over classified information to foreign intelligence agencies.

South Korea's foreign ministry confirmed the arrest.

"Upon learning of the arrest, the local diplomatic mission has been providing necessary consular assistance," the ministry said.

It declined to give further details, citing an ongoing investigation.

It marks the first time a South Korean has been arrested in Russia on spying charges.

Baek, a missionary with a South Korean humanitarian foundation, was working in Vladivostok at the time of the arrest, mostly engaged in helping North Korean defectors flee and providing them with other assistance, people with knowledge of the matter told Yonhap.

The Russian authorities had arrested Baek's wife as well but later released her. She is currently in South Korea.

Relations between South Korea and Russia have soured as Moscow has labeled Seoul an "unfriendly" country over its participation in international sanctions against Russia for its war in Ukraine.

The ties have also cooled as Russia has stepped up military cooperation with North Korea following the Sept. 13 summit between North Korean leader Kim Jong-un and Russian President Vladimir Putin.