TOKYO (KYODO) - Japan has protested Russia's plan to hold live-fire exercises in waters off one of the islands disputed between the nations, the top government spokesman said on Monday (Aug 5), as bilateral negotiations to resolve the territorial dispute remain stalled.

"We've lodged a protest through a diplomatic channel because the drills are linked to Russia's military buildup on the Northern Territories," Chief Cabinet Secretary Yoshihide Suga said at a press conference.

The protest was made last Thursday after Russia notified Japan that it would conduct six-day exercises off Kunashiri Island near Hokkaido in northern Japan from Monday, according to Japanese government officials.

Tokyo and Moscow are at loggerheads over the four islands, collectively called the Northern Territories in Japan and the Southern Kurills in Russia. The other three Russian-held islands are Etorofu, Shikotan and the Habomai islet group.

Japan lodged a similar protest in April after Russia said it would conduct live-fire drills off Kunashiri.

Despite Japanese Prime Minister Shinzo Abe's renewed push, months of bilateral negotiations have failed to achieve a breakthrough in resolving the decades-long territorial dispute that has prevented the two countries from signing a postwar peace treaty.

Last Friday, Russian Prime Minister Dmitry Medvedev visited Etorofu, his first trip to one of the disputed islands since 2015, drawing a protest from Tokyo.

Japan maintains the islands were illegally seized by the Soviet Union following its 1945 surrender in World War II, while Russia claims it legitimately acquired the islands as a result of the war.

When Mr Abe met with Russian President Vladimir Putin on the fringes of the Group of 20 summit in Osaka in late June, they agreed to continue bilateral negotiations.

The Japanese government is making arrangements for Mr Abe to attend an economic forum in Russia's Vladivostok in early September, Mr Suga said, indicating that another Abe-Putin summit may be held.

"It's because there are differences that the Japanese and Russian leaders need to meet face-to-face and hold talks," Mr Suga said.