(CNN) — Japan is demanding a formal apology from Russia after Federal Security Service (FSB) agents allegedly blindfolded and interrogated a Japanese diplomat, before giving him 48 hours to leave the country.

Foreign Minister Yoshimasa Hayashi said Vladivostok-based Japanese consul Motoki Tatsunori was detained and questioned by Russian agents on Monday for alleged espionage.

“The consular officer was taken away in a state of immobility, blindfolded from start to finish, with his hands and head held down, and subjected to intimidating interrogation,” Hayashi said during a press conference Tuesday.

Tatsunori was detained and declared “persona non grata” by Russia’s Foreign Ministry, according to Russian news agencies.

Hayashi condemned Tatsunori’s detention in the far eastern Russian city, saying it was “extremely regrettable and unacceptable” and there was “absolutely no evidence of illegal activities as claimed by the Russian side.”

Vice Foreign Minister Takeo Mori summoned Russian Ambassador Mikhail Galuzin and lodged a formal protest, demanding an official apology, Hayashi said.

The Japanese government would also be taking “appropriate measures,” he added.

Tensions between Tokyo and Moscow have been increasing, fueled by Japan’s support of Ukraine after Russia’s invasion and by the dispute between Japan and Russia over the sovereignty of islands north of Japan that were captured by Soviet forces following Japan’s surrender to Allied forces at the end of World War II.

Tatsunori had been working at the Japanese Consulate General in the Russian city of Vladivostok, a major trading port bordering China and North Korea, when he was accused by Russia of “receiving classified information.”

“A Japanese diplomat was detained red-handed while receiving classified information in exchange for money, about Russia’s cooperation with another country in the Asia-Pacific region,” the FSB said in a statement carried by Russian news agencies.

“The Federal Security Service of the Russian Federation in the Primorsky Territory stopped the espionage action of Motoki Tatsunori, Consul of the Consulate General of Japan in Vladivostok,” the report added.

In a press briefing Tuesday, Chief Cabinet Secretary Hirokazu Matsuno said Tatsunori was no longer in detention and would leave Russia by Wednesday, for his own safety.

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