Russian security officers have detained a Japanese journalist accused of collecting defense-related information for one of Tokyo’s intelligence services, the Federal Security Service (FSB) has announced.

The suspect, identified by Russia’s Foreign Ministry as Yuki Imai, worked for the Japanese newspaper Hokkaido Shimbun’s bureau in the Far Eastern Russian city of Yuzhno-Sakhalinsk and held ministry accreditation. He was detained in Sakhalin Region ahead of a planned departure from Russia and transferred to Moscow, the FSB said.

According to the agency, the correspondent gathered and stored restricted information about the number of Kuril Islands residents mobilized or volunteering to serve in the Ukraine conflict, intending to pass it to Japanese intelligence.

An FSB officer said the journalist repeatedly tasked local residents with obtaining the data despite knowing it was restricted and could not be published. The agency also said he had privately admitted to having contacts with Japanese intelligence.

The FSB released footage of the detention and documents found in the journalist’s hotel room bearing the label “For official use only.” The remaining text on the pages was blurred.

The journalist is currently being held in custody while the investigation continues.

Commenting on the arrest, Foreign Ministry spokeswoman Maria Zakharova accused Tokyo of using accredited journalists to gather information aimed at undermining Russian security, saying this was not an isolated incident.

She warned that the case would further damage bilateral relations, lamenting Japan’s “anti-Russian course” and its refusal to address Moscow’s concerns about Japanese “remilitarization.” Zakharova urged Tokyo to abandon hostile actions against Russia.

Tokyo said on Wednesday that it had requested more information about the arrest and has demanded “fair and impartial treatment” for the journalist. The Hokkaido Shimbun said it was still confirming the details, stating that ensuring the journalist’s safety was its top priority.

Relations between Moscow and Tokyo have deteriorated since Japan joined Western sanctions over the Ukraine conflict in 2022, prompting Russia to suspend peace treaty negotiations. Last month, Russia also demanded the removal of US Typhon missile systems deployed in Japan, describing them as a threat to regional security.

The countries have never signed a post-World War II peace treaty, although a 1956 declaration ended the state of war and restored diplomatic ties. A longstanding obstacle remains Japan’s claim to the four southernmost Kuril island groups, which came under Soviet control in 1945. Tokyo calls them the Northern Territories, while Moscow regards them as an integral part of Russia.