Vladimir Putin says Russia has already stationed a first batch of tactical nuclear weapons in Belarus.
The Russian president told an economic forum in St Petersburg warheads delivered to its close ally would only be used if the West threatened his country’s territory or state.
But he stressed he saw no need for Russia to resort to them for now.
US Secretary of State Antony Blinken said after Putin’s comments: “We don’t see any indications that Russia is preparing to use a nuclear weapon.”
Belarus is a key Russian ally and served as a launchpad for the dictator’s full-scale invasion of Ukraine in February last year.
Putin said transferring the tactical nuclear warheads would be completed by the end of the summer.
He added the move was about “containment” and to remind anyone “thinking of inflicting a strategic defeat on us”.
When asked by the forum’s moderator about the possibility of using those weapons, he replied: “Why should we threaten the whole world? I have already said that the use of extreme measures is possible in case there is a danger to Russian statehood.”
Tactical nuclear weapons are small nuclear warheads and delivery systems intended for use on the battlefield, or for a limited strike.
They are designed to destroy enemy targets in a specific area without causing widespread radioactive fallout.
The Russian leader is due to meet African leaders in St Petersburg after they visited Kyiv on Friday as part of a peace initiative they are presenting to both countries.
However, while they were in the city it came under Russian missile attack.
Belarusian President Alexander Lukashenko, a staunch ally of Putin, said late on Tuesday his country had started taking delivery of Russian tactical nuclear weapons that included some three times more powerful than the atomic bombs the US dropped on Japan in 1945.
