Ukraine war: Biden warns Putin not to use tactical nuclear weapons

US President Joe Biden has warned Russia not to use chemical or tactical nuclear weapons in the war in Ukraine.

Speaking during an interview with CBS News, Mr Biden said such action would "change the face of war unlike anything since World War Two".

He would not say what response the US would make to the use of such weapons.

Russian President Vladimir Putin put the country's nuclear forces on "special" alert following its invasion of Ukraine in February.

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.

Russia is estimated to have around 5,977 nuclear warheads, according to the