Japan has protested to Russia over its plan to boost troop strength on disputed islands, Japan’s top government spokesman said on Thursday, the latest move in a territorial row that has overshadowed ties since World War Two.

Chief Cabinet Secretary Yoshihide Suga told a news conference the government was closely monitoring Russia’s actions and analyzing information.

“If the move leads to the reinforcement of Russian military on the islands, it would be incompatible with Japan’s stance and it is regrettable as they are inherently our territory,” he said.

Suga made the comment after media reports that Russian Defence Minister Sergei Shoigu talked about a plan to deploy a military division to the islands, including areas Japan claims as its territory, this year.

The islands in the Western Pacific, called the Northern Territories in Japan and the Southern Kuriles in Russia, were seized by Soviet forces at the end of World War Two when 17,000 Japanese residents were forced to flee.

Suga said Russia’s military plan would be on the agenda when defense and foreign ministers from the two countries are due to meet in Tokyo on March 20.

Japanese Prime Minister Shinzo Abe and Russian President Vladimir Putin met last December and struck numerous economic deals but failed to achieve a breakthrough on the islands.

Abe is expected to visit Russia this year to speed up talks to resolve the dispute and try to conclude a peace treaty officially ending World War Two hostilities.

He has pledged to resolve the dispute in the hope of leaving a significant diplomatic legacy and building better ties with Russia to counter a rising China.