Russia’s Federal Security Service (FSB) has arrested a Japanese journalist working for the Hokkaido Shimbun newspaper on suspicion of collecting military intelligence for Japan.

The journalist was detained on Sakhalin Island while preparing to leave Russia and was transferred to Moscow, where a court ordered him held in custody for two months.

The arrest comes amid rising tensions between Russia and Japan over the disputed Kuril Islands, which Moscow controls but Tokyo claims as the Northern Territories.

Japanese Prime Minister Sanae Takaichi criticized Russian President Vladimir Putin’s recent visit to the islands, calling it unacceptable and further straining relations between the two countries, the AP has reported.

The territorial dispute dates back to World War II, and decades of negotiations have failed to produce a peace treaty, while Russia has continued strengthening its military presence in the region.