TOKYO — Japan lodged a protest with Russia on Wednesday over the arrest of a Japanese journalist on suspicion of spying, demanding that Moscow provide an explanation, consular access and humane treatment.

Russia’s Federal Security Service said the man, who works for the Hokkaido Shimbun newspaper, was suspected of gathering information about Russia’s defense capability on behalf of a Japanese intelligence agency. Russia’s Foreign Ministry identified the reporter as Yuki Imai.

The FSB, the main successor to the Soviet KGB, said it arrested the man on Sakhalin Island as he was preparing to leave Russia.

The arrest is the latest dispute between the two countries, whose tensions have spiked after President Vladimir Putin ’s visit in August to Iturup, one of four disputed Kuril Islands, a Moscow-controlled Pacific archipelago that also is claimed by Japan.

Hokkaido Shimbun said the man had been reporting in Russia on a journalist visa and was due to leave the country on Tuesday. The newspaper did not disclose his name. His latest story from the Sakhalin capital of Yuzhno-Sakhalinsk for the Hokkaido newspaper was dated Oct. 5.

Russian Foreign Ministry spokesperson Maria Zakharova said Tuesday that Imai had been charged with espionage. She accused Tokyo of using Japanese journalists in Russia to gather information to undermine Russian security, calling it “regrettable.”

Zakharova said Japan’s policies toward Russia and its military buildup threatened Moscow’s security interests in the Far East, adding that “the incident will further dampen the atmosphere in Russian-Japanese relations.”

In Tokyo on Wednesday, Kimitake Nakamura, head of the European Affairs Bureau at Japan’s Foreign Ministry, summoned Russian Ambassador Nikolay Nozdrev to protest the arrest and Moscow’s announcement without an explanation to Japan’s government, according to a ministry statement.

Nakamura demanded humane and fair treatment of the journalist and for Japanese officials to be allowed to have contact with him, the ministry said.

He also reiterated Japan’s territorial claim over the Kuril Islands, which Tokyo calls the Northern Territory. He protested a recent visit to Iturup by officials of a Chinese regional government and companies, calling it “unacceptable.” The Sakhalin regional government announced the visit Tuesday.

Nozdrev said he would relay Japan’s position to Moscow, according to the Japanese ministry.

The Committee to Protect Journalists demanded the immediate release of the journalist. “Journalists must not be used as leverage in wider geopolitical disputes,” said Fiona O’Brien, CPJ’s director for Europe and Central Asia.

At least 30 journalists are held in Russia in connection with their work, the rights group said.

Japan’s Chief Cabinet Secretary Minoru Kihara earlier said the journalist’s health was unknown because Japanese officials have been unable to contact him. Russia had not responded to Tokyo’s requests for access, he added.

“We’ll do everything we can for the protection of the Japanese citizen,” he said.

Though Japan has “many problems” with Russia, the two countries are neighbors and “we need to communicate,” Kihara said. Japan recognizes the importance of properly managing relations and will take appropriate steps to serve its national interests, he added.

The Russian region of Sakhalin includes Sakhalin Island and the four southernmost islands of the Kuril chain, which Moscow controls and Tokyo claims.

Japanese Prime Minister Sanae Takaichi protested Putin’s August visit, calling it a further blow to relations already strained by Russia’s war in Ukraine. Earlier this month, Tokyo imposed additional economic sanctions on Moscow over the war.

The Soviet Union seized the Kuril Islands from Japan in the final days of World War II. The territorial dispute has prevented the two countries from signing a peace treaty formally ending their hostilities.

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This story corrects to say the journalist was due to leave Russia on Tuesday, not Monday.