China said it was troubled by Japan's military build up and Tokyo took aim at Beijing's military ties to Russia and its suspected use of spy balloons during the Asian powers' first formal security talks in four years on Wednesday.

The talks, aimed at easing tensions between the world's second- and third-largest economies, come as Tokyo worries that Beijing will resort to force to take control of Taiwan in the wake of Russia's attack on Ukraine, sparking a conflict that could embroil Japan and disrupt global trade.

At the outset of the talks, Senior Deputy Foreign Minister Shigeo Yamada expressed concern about the suspected Chinese spy balloons and Beijing's intensifying military activities such as those in collaboration with Russia.