President Vladimir Putin's threat to use a nuclear weapon in Ukraine if Russian "territorial integrity" is threatened has sparked deep discussion in the West as to how it would respond.

"Those who are trying to blackmail us with nuclear weapons should know that the wind can also turn in their direction," Putin said, adding: "This is not a bluff."

However, analysts aren't convinced the Russian president is willing to be the first to unleash nuclear weapons since the US bombed Japan in 1945.

AFP spoke with several experts and officials about the possible scenarios that could arise should Russia carry out a nuclear attack.

What would a Russian nuclear attack look like?

Analysts say Moscow would likely deploy one or more "tactical" or battlefield nuclear bombs.

These are small weapons, ranging from 0.3 kilotons to 100 kilotons of explosive power, compared to the 1.2 megatons of the largest US strategic warhead or the 58 megaton bomb Russia tested in 1961.

Tactical bombs are designed to have a limited impact on the battlefield, compared to strategic nuclear weapons which are designed to fight and win all-out wars.

But "small" and "limited" are relative: The atom bomb the US dropped on Hiroshima in 1945 to devastating effect was just 15 kilotons.

What would Moscow target?

Analysts say Russia's goal in using a tactical nuclear bomb in Ukraine would be to frighten it into surrender or submission to negotiations, and to divide the country's Western backers.

Mark Cancian, a military expert with the CSIS International Security Program in Washington, said Russia would not likely use nuclear weapons on the front lines.

Capturing 20 miles (32 kilometers) of territory could require 20 small nuclear bombs — small gains for the huge risks of introducing nuclear weapons and nuclear fallout.