Russia reserves the right to use nuclear weapons in the event it faces aggression by Western countries, Moscow's top security official, Sergei Shoigu, was quoted as saying in an interview with the TASS state news agency on Thursday.

Shoigu's comments come as President Donald Trump and Vice President JD Vance have warned that Washington could walk away from trying to negotiate a peace settlement in Ukraine if there is no progress on a deal soon.

Since taking office in January, Trump has upended U.S. policy toward the three-year-old war, pressing Ukraine to agree to a ceasefire while easing pressure on Russia.

Shoigu, who served for over a decade as Russia's defense minister until he moved to head its powerful security council in a government reshuffle last year, cited amendments to Moscow's nuclear doctrine approved by President Vladimir Putin last November.

Under the new terms, Russia could consider a nuclear strike in response to a conventional attack on Russia or its ally Belarus that "created a critical threat to their sovereignty and (or) their territorial integrity."

"..in the event of foreign states committing unfriendly actions that pose a threat to the sovereignty and territory integrity of the Russian Federation, our country considers it legitimate to take symmetric and asymmetric measures necessary to suppress such actions and prevent their recurrence," Shoigu said.