North Korea's army has said it has approval to attack the US

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"We must assume the North Korean leadership is not crazy or suicidal in spite of bizarre things it says and does," Sung-Yoon Lee, a professor in Korean studies, has said, warning that the North's verbal attacks on South Korea and the US could be far more than just bluster and vituperation.



"Cruel, totalitarian and solipsistic the Kim dynasty surely is," he said.



"But the fact that it has managed to preserve itself for more 60 years and, in the post-Cold War era, in spite of the everyday existential threat of facing an immeasurably more successful Korean state across the border, the impoverished North has shown itself to be, if nothing else, calculating and resilient.



So, Sung-Yoon Lee asks, what is Pyongyang calculating?



"The same it has since the end of the Korean War 60 years ago," he said, speaking to CNN.



"The two constants in North Korea's foreign policy are its continual calls for the withdrawal of U.S. troops from South Korea and blaming 'U.S. hostile policy' for the tension enveloping the Korean Peninsula."



Although the North's ramped up rhetoric is not completely unusual Sung-Yoon Lee says, the country's flamboyant tirades against the South and US have certainly become more dangerous.



"Pyongyang will most likely not just go quietly into the night after having thumped its chest for so long," he said.



"We should expect some kind of deadly, although limited, attack to come soon."

North Korean leader Kim Jong-un must not be underestimated, an expert has warned

The US had better ponder over the prevailing grave situation KCNA

The news follows Prime Minister David Cameron yesterday warning that North Korea has the capability to launch nuclear weapons that could reach Britain.



The Prime Minister made the dramatic claim as he called for the UK to maintain its nuclear deterrent - insisting the threat posed by North Korea was a "real concern".



He said the actions of Kim Jong Un's regime were "worrying and threatening" and the country had "extremely dangerous" weapons.



He called for North Korea to abide by the United Nations resolution and ensure "that the heat is taken out" of the situation.



However, the North reportedly moved mid-range missiles into position for launch, yesterday – dramatically escalating its warlike rhetoric.

Images released by the North Korean Central News Agency have displayed missiles in a show of power

As tensions continued to rocket on peninsula, the North warned it had authorised plans for nuclear strikes on targets in the United States.



North Korea's military said it had ratified a “merciless attack” against the United States in a war which could start “today or tomorrow”.



In a statement, the North's supreme military command said it is formally notifying the White House and the Pentagon that "reckless operations" involving cutting-edge nuclear weapons have been finally approved.



"The moment of explosion is approaching fast," the army said in a statement on state news agency KCNA.



"The merciless operation of (our) revolutionary armed forces in this regard has been finally examined and ratified.



"The US had better ponder over the prevailing grave situation," the ominous statement concluded.



Washington has responded by reinforcing its Pacific defences – reportedly moving an advanced missile defence system to the island of Guam.



The land-based weapon, which is primed to shoot down short and medium-range missiles, is said to have been transported to the US territory to defend its bases there.



The Pentagon has already sent bombers, stealth aircraft and ships.



China has also continued to move tanks and armored vehicles whilst flying flights near North Korea this week as part of a military build-up in the northeastern part of the country that U.S. officials say is related to the crisis with North Korea.



In a dramatic twist yesterday, China reportedly rejected a request from the North to send them an envoy in order to improve their soured relations, in what could be seen as a warning regarding the regime’s recent warmongering rhetoric.