From having a more defensive policy on the use of nuclear weapons, since Putin came to power, Russia has adjusted the policy, making it more open to interpretation.
The annexation of four Ukrainian regions has further fueled the world's concern that nuclear weapons could be used in the war.
This is because the Kremlin has now stated that they consider attacks on the occupied territories as an attack on the Russian Federation.
"Raise the stakes"
- Putin has soon used all the arrows he has in his quiver.
He has now escalated, tried to annex these territories he does not fully control and threatened with nuclear weapons in a way he has done before, but not in this context, says Martin Kragh, deputy director of the Center for East European Studies.
- We are in a situation where Putin has raised the stakes.
The unpredictability has increased in a way that is alarming, says Kragh.
War scientist Oscar Jonsson, active at the Norwegian Defense Academy, is on the same track.
- I think the probability is low but it is higher than it was a few weeks ago.
When it comes to nuclear weapons, it's scary enough, says Jonsson.
See how Russia's nuclear weapons strategy has changed over the years in the clip above.