Russia has accused the United States of violating an arms control treaty by agreeing to supply anti-missile systems to Japan.
Russian Foreign Ministry spokeswoman Maria Zakharova said the deal with Japan was part of a bigger plan by the US for a "global anti-missile system."
Japan's cabinet approved a plan last week to buy two US-built Aegis Ashore missile defense systems, state broadcaster NHK reported, as the country faces increasing hostility from neighboring North Korea.
Russia has raised concerns over several US-built defense systems, claiming they also have the ability to launch missiles.
Zakharova claimed they were in breach of the Intermediate-Range Nuclear Forces (INF) Treaty, an arms control agreement between Moscow and Washington that has been in force for 30 years.
"We need to bear in mind that all these systems have universal missile launchers that can use all types of missiles. It means another violation of the INF treaty and we see that Japan is an accomplice in this matter," she said.
The US rejected the accusation. "The United States is in full compliance with the INF Treaty. Russian claims to the contrary are false and meant to deflect attention from Russia's own very clear violations," a spokesman for the US State Department told CNN.
"Third parties will not deter us from taking appropriate defensive measures in the face of growing security challenges," the spokesman added.
Zakharova's comments were the latest in a tit-for-tat between Washington and Moscow, who have accused each other of violating the INF agreement, as well as several others.
US defense officials accused Russia in March of violating the INF treaty over the deployment of a banned cruise missile.
Zakharova expressed concerns earlier this month over other US-built anti-missile systems in Romania, which she said were capable of launching missiles, and over plans for a similar system to be deployed in Poland.
She also said that the decision would strain ties between Russia and Japan. "We believe that all the actions taken by the Japanese government go against our efforts to achieve peace and security in the region. It creates mistrust between our states," she said.
North Korea has ratcheted up its missile-testing program this year, firing 23 missiles in 16 tests since February. At least two have flown over Japan.
Japan says the new US-built systems will provide coverage for the whole country.