US President Joe Biden has said that the threat of Russian President Vladimir Putin using tactical nuclear weapons is "real". 

The US president has stressed that he is concerned about Putin's possible use of nuclear weapons.

"When I was out here about two years ago saying I worried about the Colorado River drying up, everybody looked at me like I was crazy. They looked at me like when I said I worry about Putin using tactical nuclear weapons. It's real," Reuters cites Biden, who said this in a conversation with a group of donors in California.

On Saturday, Biden called Putin's statements about the deployment of the first tactical nuclear weapons in Belarus "absolutely irresponsible".

Prior to that, Putin said that the first Russian tactical nuclear warheads were already on the territory of Belarus and that the relocation would be completed by the end of the year.

US Secretary of State Antony Blinken said that there are no signs that Russia is preparing to use nuclear weapons.