Russia rebuffed as a baseless smear on Thursday a U.S. allegation that Moscow may be conducting low-level nuclear tests in violation of a moratorium.
The Ministry of Foreign Affairs said Russia was in full compliance with the Comprehensive Nuclear Test Ban Treaty (CTBT), which Moscow ratified in 2000.
It called for the United States itself to ratify the treaty.
The head of the U.S. Defense Intelligence Agency (DIA) said on Wednesday that Russia was probably not adhering to its nuclear testing moratorium in line with the "zero-yield" limit set by the CTBT.
"Such accusations are absolutely groundless and aimed at trying again to smear our country," the ministry statement said.
Negotiated in the 1990s, the CTBT enjoys wide global support but must be ratified by eight more nuclear technology states — among them Israel, Iran, Egypt and the United States — to come into force.
"We again call on the United States to show a responsible approach and to ratify the CTBT, without which its entry into force is not possible," Russia's statement said.