President Vladimir Putin, who rules the world's largest nuclear power, has repeatedly warned the West that an attack on Russia would trigger a nuclear response.

Will Putin use nuclear weapons, how many nuclear weapons does he have, and what would be the response of the United States and US-led NATO?

All about the topic:

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Isn't he bluffing?

Much depends on how Putin perceives the threat to the Russian state and to his own government, writes "24 Chasa".

Putin portrays the war in Ukraine as an existential battle between Russia and the West, which he says wants to destroy Russia and seize its vast natural resources.

Putin has warned the West that he is not bluffing when he says he is ready to use nuclear weapons to defend Russia.

Some analysts say Putin is bluffing, but Washington is taking his words seriously.

By claiming 18 percent of Ukraine's territory as its territory, Russia can now make even greater nuclear threats, as Putin can claim that attacks on those territories are an attack on Russia itself.

Merkel warned: Do not take Putin's words as a bluff!

Russia's nuclear doctrine allows the use of nuclear weapons if "aggression with conventional weapons has been carried out against the Russian Federation, which threatens its very existence."

Many Russians live in the Ukrainian territories that Putin has declared Russian, and breaking the postwar taboo on the use of nuclear weapons will not necessarily change the tactical situation on the battlefield. 

"Now he is bluffing. But what will happen in a week or a month is hard to say - when he realizes that the war is lost

," said Yuri Fedorov, a military analyst based in Prague.

"We have to take his threats very seriously, given the stakes," CIA Director William Burns said on CBS.

At the same time, however, Burns said U.S. intelligence had "no real information" that Putin was preparing to immediately use tactical nuclear weapons.

What nuclear weapons might be used?

Not a single representative of the Russian authorities calls for the use of strategic nuclear weapons, which are designed to destroy entire cities in the United States, Russia, Europe and Asia.

Ramzan Kadyrov, the president of the Chechen Republic, which is part of Russia, said Moscow should consider using low-yield tactical nuclear weapons in Ukraine.

Tactical nukes are nuclear weapons that can be used on the battlefield for "tactical" reasons and are much less powerful than the large bombs needed to destroy cities like Moscow, Washington, and London.

Such weapons can be launched from aircraft, launched by missiles from the ground, from ships and submarines, or detonated by ground forces.

Although Russia has nuclear forces that are trained to fight in such apocalyptic conditions, it is unclear how its army of regular soldiers, mercenaries, mobilized reservists and local militias will fare under such conditions.

The US does not believe that Russia is preparing to use nuclear weapons

What would the United States do?

As the world's dominant superpower, the United States will have to decide how to respond if Russia were to resort to a nuclear strike.

Russia and the US control 90 percent of the world's nuclear warheads.

Their arsenals were created during the Cold War, and modern Russia received these weapons as a legacy from the Soviet Union.

US President Joe Biden will have to choose between a non-military response, a nuclear strike that would lead to escalation, and a conventional attack that would lead Washington to a direct war with Moscow.

Jake Sullivan, the US president's national security adviser, said Washington had warned Moscow that a possible resort to nuclear weapons would have "catastrophic consequences".

Retired general and former CIA chief David Petraeus said that if Moscow were to use nuclear weapons, then the US and its NATO allies would destroy Russian soldiers and weapons in Ukraine, and sink Russia's entire Black Sea fleet.

Kremlin "will not participate in the West's nuclear rhetoric exercises"

Putin reminded Washington that so far only the US has used nuclear weapons in combat - in the 1945 attacks on the Japanese cities of Hiroshima and Nagasaki.

Who has the most nuclear weapons?

Russia has the most nuclear warheads: it has 5,977, and the United States has 5,428, according to the Federation of American Scientists.

This includes both the warheads that are available to the armed forces and those that are figuratively speaking "retired".

However, Moscow and Washington have enough warheads to destroy the world, so to speak, many times over.

Russia has 1,458 strategic warheads ready for launch, and the US has 1,389, according to the most recent figures made public.

These warheads are mounted on intercontinental ballistic missiles, submarine-launched ballistic missiles, and strategic bombers.

In terms of tactical nuclear weapons, Russia has 10 times more than the US.

About half of the US's 200 tactical nuclear weapons are based in Europe.

Former CIA director with a surprising answer on what the US will do if Russia uses nuclear weapons

US tactical nuclear weapons range from 0.3 to 170 kilotons (for reference: the nuclear bomb dropped on Hiroshima was equivalent in power to about 15 kilotons of dynamite).

Russian invasion of Ukraine