MOSCOW/TOKYO – Japan's conducting intelligence activities under the guise of journalism is "unacceptable", the Russian Foreign Ministry said Wednesday.

"This is not an isolated incident," spokeswoman for the ministry Maria Zakharova said. "Similar cases have occurred quite recently."

Russia's Federal Security Service announced Tuesday local time that it had detained a Japanese correspondent on suspicion of espionage. The correspondent worked at the bureau of the Japanese newspaper Hokkaido Shimbun in Yuzhno-Sakhalinsk, the administrative center of the Sakhalin region.

According to Russian media, the correspondent was detained in Sakhalin as he was about to leave Russia and was subsequently transferred to Moscow. The case remains under investigation.

READ MORE: Russia detains Japanese correspondent on espionage charges

Zakharova said Tokyo's attempts to use its correspondents stationed in Russia to collect intelligence were regrettable and further undermined Russia-Japan relations. 

On Wednesday, Japan's Foreign Ministry summoned Russian Ambassador to Japan Nikolai Nozdrev.

According to a statement released by the ministry, Japan requested that the Russian side provide information about the case promptly and that the detained Japanese national be treated in a humane, fair and impartial manner.

The ministry said the Japanese government has so far received no explanation from the Russian side regarding the detained Japanese national.