At a nuclear nonproliferation conference, Russian diplomat Alexander Trofimov rejected "utterly unfounded, detached from reality and unacceptable speculations that Russia allegedly threatens to use nuclear weapons, particularly in Ukraine", Reuters reported.
Within days of the Feb 24 start of the Russia-Ukraine war, Russian President Vladimir Putin put the country's deterrence forces - which include nuclear arms - on high alert, citing aggressive statements by NATO leaders and Western economic sanctions against Moscow.
Trofimov, a senior diplomat in the non-proliferation and arms control department of Russia's foreign ministry, said Moscow would only use nuclear weapons in response to weapons of mass destruction or a conventional weapons attack that threatened the existence of the Russian state.
"None of these two hypothetical scenarios is relevant to the situation in Ukraine," Trofimov told the UN conference to review the Treaty on the Non-Proliferation of Nuclear Weapons.
However, he accused NATO countries of a "fierce hybrid confrontation" against Russia that now "dangerously balances on the edge of open military clash."
"Such a move would be able to trigger one of the two emergency scenarios described in our doctrine," Trofimov said. "We obviously stand for preventing this, but if Western countries try to test our resolve, Russia will not back down."
Russia on Tuesday accused the United States of direct involvement in the Ukraine war.
Moscow said it was responding to comments by a Ukrainian official about the way Kiev had used US-made and supplied High Mobility Artillery Rocket System (HIMARS) launchers based on what the official called excellent satellite imagery and real-time information.