Chinese and Russian military officials are likely to have agreed to strengthen their surveillance activities to boost "strategic deterrence against Japan," sources close to the matter said Thursday, reflecting a recent deterioration in Beijing and Moscow's relations with Tokyo.

But China and Russia have also decided not to carry out joint surveillance around Japan for the time being, the Chinese sources said, adding such agreements were made during an online meeting in June between senior military officials of the two countries.

Beijing and Moscow are expected to increase military activities in waters surrounding the Japanese archipelago, including the East China Sea, as they have been at odds with Tokyo over Taiwan — which China regards as a renegade province — and Russia's invasion of Ukraine, foreign affairs experts said.