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.
“You think I would tell you if I knew exactly what it would be? Of course, I’m not gonna tell you. It’ll be consequential,” Mr Biden responded.
“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 north-eastern Kharkiv region.