The Russian foreign ministry said on Thursday that Moscow has no interest in a direct confrontation with NATO and the United States and it had no need to use nuclear weapons during its military campaign in Ukraine.
The ministry dismissed media speculation that Moscow might deploy nuclear or chemical weapons in the conflict as "absolute lies."
Speaking at a briefing on Thursday, Foreign Ministry spokesman Ivan Nechayev, whose role is to act as a mouthpiece for the Kremlin, said nuclear weapons would be used solely as a "response" measure.
He said: "Russian military doctrine allows a nuclear response only in response to the threat of mass destruction, or when the very existence of the state is threatened.
"That is, the use of a nuclear arsenal is possible only as part of a response to an attack in self-defence and only in emergencies."
Fears of a nuclear crisis in Ukraine have been heightened recently amid a stalling offensive by the Russians and reports they are using a seized nuclear power plant as a military base.
On Thursday, Russia rejected a proposal by UN Secretary-General Antonio Guterres to demilitarise the area around the Zaporizhzhia nuclear power plant, saying it would make the facility "more vulnerable".
The plant, Europe's largest of its kind, was captured by Russia in March, shortly after President Vladimir Putin ordered tens of thousands of troops into Ukraine in what he called a "special military operation."
Fears have grown in recent weeks over its safety and the risks of a possible Fukushima-style nuclear accident after Ukraine and Russia accused each other of shelling it.
Guterres, who is currently on a visit to Ukraine, earlier this month called for the withdrawal of military personnel and equipment from the power station and for "a safe perimeter of demilitarisation."
Nechayev accused Kyiv, without evidence, of organising what he called provocations and of being unable to control nationalist armed groups.
"That is the very reason that the proposals (on demilitarisation) are unacceptable," said Nechayev.
"Implementing them would make the power station even more vulnerable."
Russia claims it keeps some troops at the plant to ensure its smooth running and security.
Kyiv accuses Russia of using the plant as a shield from which it shells Ukrainian targets.
Nechayev said a visit to the plant by the International Atomic Energy Agency (IAEA) could take place in the very near future and that experts could determine for themselves who had been shelling it.