Russia test-fired anti-ship missiles from an island which is also claimed by Japan, a week after Vladimir Putin angered Tokyo by becoming the first Russian president to visit the disputed archipelago.
The Pacific Fleet said on Thursday a unit equipped with the Bastion coastal missile system, which is stationed on Etorofu, simulated an attack on enemy warships and hit all its targets at a range of about 300km.
A guided missile cruiser and a nuclear-powered submarine took part, according to reports.
"We cannot tolerate moves to strengthen military power on the Four Northern Islands because they go against our country's stance on the territories," Japanese foreign minister, Toshimitsu Motegi, said during a visit to Oman.
The firing formed part of exercises that began on 4 August and are due to run until 29 August, involving about 60 surface ships, submarines, support vessels, some 30 aircraft, helicopters, drones, and more than 13,000 personnel, according to the Russian state news agency Tass. Japan was told in advance that they would include live firing and lodged a protest on 5 August.
Mr Putin watched part of the exercises from the deck of the Varyag, the fleet's flagship, on 12 August, before visiting Etorofu the following day. Speaking aboard the cruiser, he said the region was becoming more prone to conflict.
"Nato seeking to gain a foothold here and the emergence of new military and political blocs," he said. "There are efforts and plans to deploy new weapons systems here, which creates threats for our country."
His visit to the island, the first by a Russian president, prompted a protest from Tokyo and a tit-for-tat summoning of ambassadors in both capitals.
The islands lie off the eastern coast of Hokkaido, Japan's northernmost main island, and comprise Etorofu, Kunashiri, Shikotan and the Habomai group.
Japan calls them the Northern Territories, Russia counts them as part of the Kuril chain, and the dispute over them goes back to the 19th century.
The then Soviet Union took the islands from Japan in the closing days of the Second World War, and because the argument has never been settled, the two countries have never signed a peace treaty formally ending the war between them.
Relations have deteriorated sharply since Russia's full-scale invasion of Ukraine in 2022, after which Japan joined its Group of Seven partners in imposing sanctions on Moscow.
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