What are tactical nuclear weapons and could Russia use them in Ukraine?

Over the past month, Russia has repeatedly waved the threat of nuclear force to deter the West from meddling in the war in Ukraine.

This week, the Kremlin’s spokesman refused to rule out the use of nuclear weapons, saying they could be used if the country faced an "existential threat".

The head of the Russian space agency also issued an ominous warning, saying "the Russian Federation is capable of physically destroying any aggressor or any aggressor group within minutes at any distance".

The comments - which follow President Vladimir Putin’s order last month to put Russia’s deterrence forces on special alert - have alarmed the West, and top US government officials say the White House is now mapping out how it could respond should Russia use weapons of mass destruction.

So, how close is Russia to unleashing its atomic arsenal? And how destructive could it be?

Nuclear weapons have never been used in a war since 1945, when the two atomic bombs dropped by the United States on Hiroshima and Nagasaki devastated the Japanese cities and instantly killed tens of thousands of people.

"That's a 76-year tradition of non-use of nuclear weapons. And that is the single most important feature of the nuclear age, and we really want to keep it that way," Nina Tannenwald, senior lecturer in international relations at Brown University in the US, told Euronews Next.

The horror of the bombings shocked the world into the age of nuclear deterrence, where global powers raced to develop such weapons, all the while knowing that their use would be catastrophic for humanity - and thus refraining from wielding them against one another.

Nowadays, Russia has the world’s largest nuclear arsenal with around 6,257 nuclear warheads, while the United States admits