Japanese Foreign Minister Taro Kono says the government has lodged a protest with Russia over its ongoing military drills on and around the island of Kunashiri. Japan claims the island as part of its Northern Territories.
The Russian military has said the military drills will continue through Sunday, involving more than 2,000 troops.
Kono told the Lower House budget committee on Wednesday that the exercises could lead to a Russian military buildup on the 4 islands, including Kunashiri, in Japan's Northern Territories.
Russia controls the islands. Japan claims them.
The Japanese government maintains the islands are an inherent part of Japan's territory. It says the islands were illegally occupied after World War Two.
Kono said the Russian military drills are incompatible with Japan's position.
To fundamentally resolve such a problem, the foreign minister said, it's necessary to settle the territorial issue and sign a peace treaty with Russia. He said the government will persistently continue negotiations for that purpose.
Also at the budget committee, Defense Minister Itsunori Onodera briefed on Monday's fatal helicopter crash in Saga Prefecture, western Japan.
He suggested his ministry will hear the opinions of experts, the manufacturer of the aircraft and those in charge of maintenance to determine the cause of the accident.