"We confirmed that Russian military bombers and fighter jets flew over the high seas of the Sea of Okhotsk and the Sea of Japan yesterday, and we scrambled Air Self-Defense Force fighter jets" in response, Yoshimasa Hayashi told reporters.

"It is difficult to say clearly what the purpose of the flight was... but the Russian military has been active on an ongoing basis in areas surrounding Japan," he said.

Tokyo has raised the issue with Moscow in the past through diplomatic routes, including regarding a Russian fighter jet's intrusion into territorial airspace in September, which Russia denied according to media reports.

"We will continue to monitor (the situation) closely and do our best to take measures in patrolling and responding to airspace incursions," Hayashi said.

Russia's defence ministry said on Telegram Thursday that two long-range bombers flew over international waters in the Sea of Japan and the Sea of Okhotsk.

The Russian ministry also released a video of two Tupolev-95 aircraft escorted by Russian fighter jets conducting what it called a regular flight over more than eight hours.

"All flights by Russian Aerospace Forces aircraft are carried out in strict compliance with international rules on the use of airspace," it said in a statement.