North Korea’s top diplomat said President Donald Trump’s tweet that leader Kim Jong Un “won’t be around much longer” was a declaration of war against his country by the United States.

Foreign minister Ri Yong Ho told reporters that Mr Trump’s statement gives North Korea “every right” under the UN Charter to take counter-measures, “including the right to shoot down the United States strategic bombers even though they’re not yet inside the airspace border of our country”.

Mr Ri referred to Mr Trump’s tweet Saturday which said: “Just heard Foreign Minister of North Korea speak at U.N. If he echoes thoughts of Little Rocket Man, they won’t be around much longer!”

Mr Ri said: “The question of who won’t be around much longer will be answered then.”

The foreign minister opened his brief remarks in Korean by saying that over the last few days, the UN and the international community have clearly wished "that the war of words between the DPRK (North Korea) and the United States will not turn into real action".

He said: "However, that weekend, Trump claimed that our leadership wouldn't be around much longer, and ... he declared the war on our country.

"Given the fact that this comes from someone who is currently holding the seat of (the) United States presidency, this is clearly a declaration of war."

He said all UN members and the world "should clearly remember that it was the US who first declared war on our country".

Mr Ri then said North Korea now has the right to retaliate against US bombers.