North Korea has been secretly training elite special forces to kidnap Westerners from South Korea and hold them hostage in the event of any conflict.
If the United States attacks the so-called Hermit Kingdom, snatch squads armed with deadly nerve agents are poised to slip past South Korean border checkpoints to grab diplomats, tourists and foreign businessmen.
In an exclusive interview, Ung-gil Lee, who defected to South Korea after serving for six years in one of these clandestine units, told The Mail on Sunday: "The best case [for his old unit] would be to round them up and take them north, but if not they will take the foreigners hostage in South Korea.
"But they will all be killed, come what may - this goes hand in hand with assassination."
North Korea has a history of abducting foreigners. In the 1970s, South Korea's leading movie star Choi Eun-hee and foremost director Shin Sang-ok were held as prisoners to make films for the brutal totalitarian regime until they escaped seven years later, reports Daily Mail.
The Mail on Sunday's revelation of the terror units comes as tensions rise over North Korea's growing nuclear strength.
US President Donald Trump pledged to "take care" of the issue following his surprise cruise missile attack on Syria over its use of chemical weapons.
Trump has sent a naval strike group, including an aircraft carrier and submarines, to the region.
Kim Jong Un, the North Korean dictator, responded by warning he is "ready to react to any mode of war desired by the US".
Lee, a former corporal in the 11th Storm Corps, says his former comrades have been trained to carry out Islamic State-style terror attacks.
The 37-year-old, who now works as a financial adviser in Seoul after defecting from the repressive regime in 2006, warns that if attacked, Kim Jong Un will respond very differently from Syria's President Bashar Assad: "He is going to fight back and use all retaliatory measures. Unless Trump thinks he can get rid of him, he must not carry out an attack."
Lee was recruited to join North Korea's infamous special forces aged 17. Following one year of brainwashing "re-education", he spent five years training as a communications officer.
The nation is thought to have 200,000 men and women in the world's biggest special forces, with 140,000 in infantry groups and 60,000 in Lee's 11th Storm Corps.
They are renowned for extreme training that includes boxing fights before dinner every night, punching trees and swimming in freezing seas.
Elite units are trained to infiltrate South Korea by air, sea and through a network of tunnels built by forced labourers.
Lee says he was part of a 100-strong land and air group selected for raids on the South to destroy infrastructure, disrupt roads and ports, and kidnap foreigners.
"We would sneak into the South, change our clothing, go into areas where there are lots of foreigners and capture some of them. We memorised locations, phone numbers and the car number plates of major embassies."
His group was also taught to memorise details about mobile phone systems - and were armed with nerve agents along with conventional weapons.
"I carried neostigmine bromide and potassium cyanide. Those exposed to these drugs die of heart attacks. These were carried for attacks or else for us to commit suicide."
Neostigmine bromide is five times more toxic than potassium cyanide.
North Korean agents have previously used tiny guns or pens loaded with the drug, which has been detected in the killing of a South Korean diplomat and the assassination attempt of a leading dissident.
"These were suicide missions," says Lee of his excursions into the South. "Obviously we were supposed to go back but, if not, we were told we must kill ourselves."
There are several of these squads, each assigned a different region of South Korea. Lee's unit - which he says still exists, although its number changes frequently to avoid detection - focused on Pohang, a port of half a million people.
Twice a year they would have sessions to hone training, and every other year hold a major exercise in an area in North Korea most similar to their target city.
Prizes of party membership, which entitles holders to perks and privileges, were offered to the most tenacious operatives.
The former corporal's view that Trump can risk attack on North Korea only if he can kill its 33-year-old leader echoes other experts.
They fear that otherwise, risks of conflagration are too high, even if strikes are limited to the nuclear test facilities.
North Korea has ramped up weapons development under Kim Jong Un.
Last year alone it carried out two nuclear tests, 24 missile tests and the trial of a new high-thrust missile engine. Experts fear the rogue regime is close to being able to strike the US mainland.
It has substantial stockpiles - thought to be up to 5,000 tons - of chemical weapons.
North Korea has 1.2 million in its armed forces and almost eight million in reserve, while South Korea has barely half the numbers but far better weapons - plus the support of 28,500 US troops.
China, the North's strongest ally, is reported to have moved 150,000 troops to its border with North Korea.
Lee admits that during his military years he believed in his duty to protect the dynastic dictatorship that has ruled North Korea for seven decades.
It uses supposed threat of attack by South Korea and the US to retain power and excuse its poverty and repression.
But he lost his faith after being sent to university by his superiors - he saw smuggled foreign films that shattered the propaganda pumped out behind the Bamboo Curtain.
He says: "The first American film I saw was Saving Private Ryan. I was amazed.
"I was taught that only our soldiers had a sense of brotherhood and honour but I saw these Americans with an immense sense of love, honour and brotherhood. I began thinking that maybe all I had been taught in the army was false."
He also started to meet Chinese traders, eventually bribing his university £220 a month to bunk off studies so that he could start smuggling the narcotic crystal meth to China and other goods back to his homeland. Finally he defected to Seoul with his wife and sister.
Once he was prepared to die for North Korea. But the more Lee learned about the regime, the angrier he became.
"It is right to call North Korea part of the Axis of Evil," he says.
"Its leader is worse than all the evil dictators of Libya, Iraq and Syria combined."
War drums are beating - and Britain appears so impotent
Comment by Michael Burleigh
Right around the points of the compass, the war drums are beating again. President Trump has "turned on a dime", as they put it, reversing the isolationist promises that won him the US election.
USS Carl Vinson and its escorts are heading for Korean waters, where Kim Jong Un may conduct his sixth nuclear test.
On Thursday, the American military heaved "the mother of all bombs" out of a plane to destroy a unit of IS's most dangerous affiliate in Afghanistan.
Before that, cruise missiles pounded the Syrian air base from which chemical strikes were allegedly launched. American tensions with Russia and Iran have increased sharply.
And where is Britain in all this? The answer is nowhere.
Increasingly detached from Europe, the only power bloc that could give us real significance for the future, we are looking isolated and ineffectual, as the humiliating G7 rejection of Boris Johnson's ill-considered plans to increase sanctions on Russia made clear.
You might say this has been coming for a while as Britain's post-war influence steadily declined.
Many commentators have revisited US Secretary of State Dean Acheson's cutting witticism, delivered in 1962, that Britain had lost an empire - but had not yet found a role.
Of course, this is unfair to successive generations of extremely capable British diplomats, not to mention Foreign Secretaries of real distinction such as Lord Carrington or David Owen. There are times when our diplomacy was both extremely good and effective.
Britain sought to protect its interests through membership of several overlapping circles: the North Atlantic Alliance, the Commonwealth and the EU.
It is half a century ago, but we even had a Prime Minister brave enough to decline involvement in American wars of choice.
In 1964, Harold Wilson refused to send 'even a bagpipe band' as President Lyndon Johnson put it (referring to the Black Watch) to Vietnam.
But now this patiently constructed approach is unravelling. Under Blair, then Cameron, we have been in thrall to the concept of Britain as a "transatlantic bridge" between Europe and the US.
But that was ill-advised and doomed to failure ever since 2003, when Blair attached himself like a limpet to the belligerent George W. Bush, while major European powers declined to support his war in Iraq.
Even clinging to the coat-tails of America looks unrewarding - and no wonder. President Trump's policies seem to chop and change according to the President's whims.
For months Trump signalled he wanted to repair relations with President Putin, while declaring a trade war against China.
For weeks he has been saying that the ousting of President Assad is no longer a priority. Now he wants this "animal" out as fast as possible.
After sharing Dover sole, steak, and chocolate dessert with President Xi Jinping, there was no more talk of a trade war.
There are those, of course, who believe in a successful British future in an "Anglosphere" of the English-speaking democracies, but this is a pipe dream.
The brute reality is that Australia is very far away, does little trade with us, and is preoccupied with a Pacific region in which China is its biggest customer for its coal and minerals.
How close do we wish to be to India, a democracy in name only? Some 163 Indian MPs are currently charged with murder, rape and kidnapping.
We have friends in the Gulf, but do we really want to get in bed with Qatar (home of the Muslim Brotherhood), or despotic Saudis?
There are chronic problems with our foreign policy, and now Brexit has thrown them into sharp relief.
Never before has our impotence been so clearly exposed on the world stage.
With true global forces such as America and China - and wannabe world powers such as Russia - openly bidding to shape the world their way, Britain is in a very lonely world.