Donald Trump has warned that the deployment of America's 'monster' nuclear weapons 'could happen tomorrow', in what appears to be a veiled threat to Washington's enemies as the world teeters on the brink of a global war.

The B-83 is the most powerful weapon in the United States' nuclear arsenal, capable of inflicting untold damage on civilian populations and wiping out entire cities.

The destruction it would unleash if it were deployed would be on a scale never seen before - with the 1.2 megatonne payload making it some 75 times more powerful than the nuke detonated over Hiroshima. 

Estimates put the number killed in the 1945 bombing at around 140,000, while projections for the number of people who would lose their lives if the B-83 were dropped on a major city stand in the millions.

The radiation released by such a bomb depends on where it explodes, but also whether it detonates on the ground or in the air, with the earth absorbing around half of it in a surface blast while a low-air blast would maximise the devastation.

In an airburst, the B-83 would release a fireball measuring more than one and a half square miles, decimating everything in this area, according to a model produced by nuclear technology historian Alex Wellerstein.

The radioactive fallout would also spread out for miles, with everyone within a roughly eight-mile radius being exposed to a 500 rem ionising radiation dose - enough to prove fatal for the majority of those exposed to it within a month.

The powerful weapon would be able to eradicate underground bunkers near the epicentre and would severely damage or entirely demolish concrete buildings within the heavy blast zone, which would cover a roughly 6.5 square miles.

Fatalities in this area would be near 100 per cent. Further out in the 'moderate' blast zone, most residential buildings would collapse and many people would lose their lives, with all sustaining injuries.

Thermal radiation would cover an area of more than 210 square miles - meaning everyone in this area who wasn't instantly killed would suffer life-changing third-degree burns, as well as radiation sickness in many cases.

If, for whatever reason, Washington chose to drop the B-83 on Moscow, some 1.3million people would be killed and more then 3.7million injured.

The world famous Bolshoi Theatre, Red Square and the Kremlin - Vladimir Putin's seat of government - would be obliterated by the initial fire ball, which would wipe out much of the city's historic buildings as well as more modern concrete blocks.

There would be a similar death toll of around 1.3million in Pyongyang if the centre of North Korea's capital was targeted, with the Hermit State's Juche Tower and Arch of Triumph among the monuments which would be eradicated.

Meanwhile some 1.5million people would lose their lives if Beijing were hit, with Tiananmen Square being, the Forbidden City and the Communist Party Headquarters all destroyed by fire and the force of the impact.

Casualties would be even higher in Tehran, according to Professor Wellerstein's projections, with 2.6million potentially losing their lives and 3.7million injured.

If the centre of the Iranian capital was hit, the historic Golestan Palace and its surroundings would be burned down instantly, while the Azadi Tower slightly further out of the city would likely be damaged or destroyed if the immense heat resulted in fires breaking out in the area.

The B-83's deadly potential - with the weapon being the last megatonne bomb in the US arsenal - has prompted numerous attempts to get it decomissioned since it came into service in 1983.

Former President Barack Obama sought to get rid of the bomb, but his decision to do so was reversed by President Trump in his first term in office.

Joe Biden then revived efforts to get rid of the nuke, but was met with staunch opposition from Republican lawmakers who argued that the weapon was needed to strike deeply buried targets.

Now Trump has warned that nuclear weapons pose the greatest threat to humanity, suggesting in an interview yesterday that US warheads are capable of 'ending the world' in an apparent reference to the principle of mutually assured destruction.

Trump, who has the world's second-largest nuclear stockpile at his disposal after Russia's Putin, made the shock statement in an interview last week.

'We spend a lot of money of nuclear weapons - the level of destruction is beyond anything you can imagine,' he told Fox News.

'It's just bad that you have to spend all this money on something that if it's used, it's probably the end of the world.'

The Republican added that the threat of climate change was nothing compared to the risks posed by nuclear weapons, claiming that a nuclear war 'could happen tomorrow.'

Trump explained: 'I watched Biden for years say the existential threat is from the climate. I said 'no'.

'The greatest is sitting on shelves in various countries called 'nuclear weapons' that are big monsters that can blow your heads off for miles and miles and miles.'

Despite previously preventing the US stockpile being scaled back, Trump has signaled during the first weeks of his second presidential term that he is keen to reduce the number of nuclear weapons in the world. 

It is unclear if this is his administration's official position.

The President last week revealed that he had sent a letter to Iran's top authority pressuring them to strike a nuclear deal, while also threatening military action if one was not reached.

'There are two ways Iran can be handled, militarily or you make a deal. I would prefer to make a deal,' Trump told Fox News.

'I would rather negotiate a deal. I'm not sure that everybody agrees with me, but we can make a deal that would be just as good as if you won militarily,' Trump said. 

'But the time is happening now, the time is coming up. Something is going to happen one way or the other. I hope that Iran, and I've written them a letter, saying I hope you're going to negotiate because if we have to go in militarily it's going to be a terrible thing for them.' 

Trump pulled out of the Iran nuclear deal in 2018 during his first term in office. 

Last month, Trump said he was willing to reopen arms controls negotiations with both China and Russia.

He said at the White House: 'There's no reason for us to be building brand new nuclear weapons. We already have so many.

'You could destroy the world 50 times over, 100 times over. And here we are building new nuclear weapons, and they're building nuclear weapons.'

He added: 'We're all spending a lot of money that we could be spending on other things that are actually, hopefully, much more productive.'

While the US currently has 5,177 nuclear warheads, including 1,477 waiting to be dismantled, this is a far cry from its peak stockpile of 31,255 warheads in the late 1960s.

Little Boy, the name given to the L-11 nuclear bomb which was dropped on Hiroshima and the first to ever to be used in warfare, has a payload of just 15 kilotonnes - a fraction of the destructive potential of the B-83.

The dropping of nuclear bombs on the Japanese city and Nagasaki three days later in the final days of World War Two mark the only time nuclear weapons have been used in combat to date.

But with an increasingly volatile global security situation, deemed by many analysts to be the worst such crisis since the Cold War, rhetoric about the possible use of these indiscriminate weapons has been ramping up in Washington, Moscow and other nuclear-armed states around the world.