Japan's top government spokesperson says Tokyo is watching planned joint military exercises by China and Russia with grave concern.

China's defense ministry announced on Monday that Russian forces will take part in the Chinese military exercises in the Sea of Japan and that the Chinese navy will participate in Russia's naval drills in the Pacific.

Speaking to reporters on Wednesday, Japan's Chief Cabinet Secretary Hayashi Yoshimasa said it is difficult to assess the intentions and purposes of these exercises.

He pointed out that in recent years, China and Russia have engaged in joint training with naval vessels and bombers.
He said Japan views the upcoming exercises as part of the two countries' efforts to bolster their military alliance.

Hayashi said Japan will continue to gather and analyze information, and do its utmost in its monitoring and surveillance activities.