Russia has been cautioned not to use chemical or tactical nuclear weapons in the conflict in Ukraine by US Vice President Joe Biden.
This will “alter the face of battle unlike anything since World War Two,” Mr. Biden said in an interview with CBS News.
He remained mum regarding the US’s response to the use of such weapons.
After its invasion of Ukraine in February, Russian President Vladimir Putin put the nation’s nuclear forces on “special” alert.
He told defence chiefs it was because of “aggressive statements” by the West.
Nuclear weapons have existed for almost 80 years and many countries see them as a deterrent that continues to guarantee their national security.
It, however, remains unlikely that it intends to use such weapons.
Tactical nuclear weapons are those which can be used at relatively short distances, as opposed to “strategic” nuclear weapons which can be launched over much longer distances and raise the spectre of all-out nuclear war.
In an interview with CBS’ 60 Minutes correspondent Scott Pelley in the White House, President Biden was asked what he would say to President Putin if he was considering using weapons of mass destruction in Ukraine.
“Don’t, don’t, don’t,” was President Biden’s response.
Mr Biden was then asked what the consequences would be for Mr Putin if such a line was crossed.
“They’ll become more of a pariah in the world than they ever have been. And depending on the extent of what they do will determine what response would occur.”
The war in Ukraine has not gone as well as the Kremlin had hoped.
In recent days, Ukraine says it has recaptured more than 8,000 sq km (3,088 sq miles) of territory in the northeastern Kharkiv region.
Despite the apparent setback, President Putin has insisted that Ukraine’s successful counter-offensive will not stop Russia’s plans of continuing its operations in the east of the country.