Russia accused Japan on Thursday of abandoning decades of pacifist policy and embracing "unbridled militarization", responding to a $320-billion defence plan announced by Prime Minister Fumio Kishida last week.
"It can be clearly seen that Tokyo has embarked on the path of an unprecedented build-up of its own military power, including the acquisition of strike potential," the Russian Foreign Ministry said in a statement.
Kishida's plan will double defence outlays to about 2% of gross domestic product over five years and make Japan the world's third-biggest military spender after the United States and China.
It reflects Japan's concern that Russia's invasion of Ukraine sets a precedent that will encourage China to attack Taiwan.
"This is a frank rejection by the F. Kishida administration of the peaceful development of the country, which was persistently declared by previous generations of politicians, and a return to the rails of unbridled militarization," the Russian statement said.
Russia said such a move will "inevitably provoke new security challenges and will lead to increased tension in the Asia-Pacific region".
In a further dig at Tokyo, it said the defence spending increase was taking place despite "the far-from-brilliant state of the national economy and growth of structural imbalances in the state budget".
Relations between Tokyo and Moscow have been long been overshadowed by an unresolved dispute over a group of Pacific islands seized by Soviet troops from Japan at the end of World War Two.
They have plummeted further since Russia invaded Ukraine in February, prompting Japan to join its Group of Seven (G7) partners in imposing sanctions on Moscow.
