A Russian nuclear strike would change the course of the conflict in Ukraine and would almost certainly trigger a "physical response" from Ukraine's allies and possibly from NATO, a senior NATO official said, Reuters reports.

According to the official, any use of nuclear weapons by Moscow would have "unprecedented consequences" for Russia. He said it would "almost certainly be drawing a physical response from many allies, and potentially from NATO itself."

The official added that Moscow used its nuclear threats mainly to deter NATO and other countries from directly engaging in war in Ukraine.