Russian Foreign Minister Sergei Lavrov said on Thursday that Russia was only operating on its own territory after Japan accused Moscow of a military buildup on a chain of islands in the Pacific, the state-run RIA news agency reported.

Russia has held the islands — known as the Northern Territories in Japan and the Southern Kurils in Russia — since World War II and they are a reason the two countries have not formally ended hostilities since the war.

Speaking in Tokyo at talks with the Japanese foreign and defense ministers, Lavrov was quoted as saying that Moscow was concerned by U.S. missile deployment plans in Japan.