World War 3: Time is running out to prevent military conflict exploding in Korea

And the conflict would cause as many casualties as the Vietnam or Iraq Wars – even without nuclear weapons – said the Royal United Services Institute.

The pressure for US action is growing because North Korea’s nuclear threat is developing every day.

The report, by Professor Malcolm Chalmers, said: “Some of Trump’s key advisers may believe … that it is now or never for the US to take military action.”

He said the UK must urge the US to reject plans for a pre-emptive strike and instead push for a solution through sanctions and diplomacy.

But he said that if the US did decide to attack North Korea, the UK would have to decide almost instantly where it stood.

Prof Chalmers, who advised the Blair Governments on foreign affairs, wrote: “The UK government would have, at most, only a few hours to make clear how it stood on what would be one of the most momentous strategic shocks of the post-Cold War era.

“Its decision would have as profound an impact on the UK’s international standing, and on its domestic politics, as the fateful decision to stand ‘shoulder to shoulder’ with the US in the run up to the 2003 invasion of Iraq.”

“But there would be no time for multiple consultations and deliberations before positions had to be taken. The die would be cast on Day One.”

The report was issued with the war of words between North Korea and President Trump getting ever more ominous and lurid.

North Korea has defied the UN by developing a nuclear weapons programme, setting off its sixth and biggest nuclear bomb earlier this month.

The rogue state’s leader Kim Jong Un claims to have Intercontinental Ballistic Missiles which can hit the mainland US with nuclear warheads.

In recent weeks it has test fired missiles over Japan and threatened to target the US island of Guam in the western Pacific.

On Monday North Korea’s Foreign minister Ri Yong Ho accused America of having already declared war on his homeland.

President Trump has mocked Kim as “Little Rocket Man” and vowed to respond to any threat with “fire and fury”.

And on Tuesday he said the US is “totally prepared” for military action, adding: “If we take that option it will be devastating — devastating — for North Korea. It’s called the military option.” 

Prof Chalmers, the RUSI Deputy Director General wrote: “War is now a real possibility. With North Korea making rapid progress in its missile and nuclear programmes, time is not on diplomacy’s side.”

He said: “The US is prepared to maintain the option of preventive strikes against North Korean nuclear facilities despite the knowledge that these could result in a new Korean war, perhaps comparable in scale and loss of life with the conflicts in Iraq or even Vietnam. 

“The war could start in a variety of ways: North Korea could strike first if it believed that the US were moving towards a surprise attack; or a US attack might be triggered by North Korean test missiles hitting the ocean near Guam or California.”

He said that if war is launched “it will not be surgical or short”.

Casualties would rise if North Korea was able to unleash a nuclear attack on South Korea or Japan before its forces were overrun, or if the pariah state’s only real ally, China, became directly involved in the fighting. 

Prof Chalmers said war would be likely to involve an early large-scale US-led air and cyber offensive, followed by retaliation by Pyongyang against South Korea – where around 8,000 Britons live – and American bases in the region using conventional, chemical or nuclear weapons.

That would mean a full-scale invasion of the state would be highly likely.

Prof Chalmers continued: “While the broader political and economic effects of such a conflict are highly unpredictable, they are likely to be global in nature, dwarfing the effects of the 9/11 attacks and their aftermath in Afghanistan and Iraq. 

“For the two Koreas, casualties could run into the hundreds of thousands. China and Japan, the world’s second- and third-largest economies, could face severe disruption to their societies, especially if nuclear weapons were used or if a conventional war were to last for several months. 

“US leaders also know that a war could put 60,000 American troops based in the region at risk, along with many tens of thousands of American civilians.”

Given that any attack on Pyongyang would be likely to trigger North Koran retaliation against South Korea, Prof Chalmers a US preventive strike without South Korea’s agreement would show that Washington was willing “to sacrifice Seoul to protect New York”.

But military analyst, Major Charles Heyman, played down the risk of war.

He said: “I do not think there’s a huge risk of war breaking out. A good indicator is that the markets are pretty stable, especially in south east Asia.

“There’s a lot of posturing going on but it does look like the protagonists are stepping back from the brink.

“Some reasonably wise heads in Washington are pulling Trump back and some reasonably wise heads in China are having a quiet word with Kim Jong Un.

“If there was a war, North Korea would be destroyed and a huge number of American lives would be lost, and both sides know that.”

British sources said the UK’s focus is to work with its allies to pressure Pyongyang to enter into negotiations over the denuclearisation of the Korean Peninsula.