The White House has dismissed as “absurd” the suggestion by North Korea’s foreign minister that the United States has declared war on Pyongyang.

Ri Yong Ho said President Donald Trump had declared war on North Korea and that Pyongyang reserved the right to take countermeasures, including shooting down US bombers even if they are not in its air space.

Mr Ri said a Twitter message by Mr Trump in which the president warned that the minister and North Korean leader Kim Jong-un “won’t be around much longer” if they acted on their threats amounted call for war.

“We’ve not declared war on North Korea. Frankly, the suggestion of that is absurd,” White House spokeswoman Sarah Sanders said.

Earlier in New York, where he had been attending the annual UN General Assembly, Mr Ri told reporters: “The whole world should clearly remember it was the U.S. who first declared war on our country.”

“Since the United States declared war on our country, we will have every right to make countermeasures, including the right to shoot down United States strategic bombers even when they are not inside the airspace border of our country.

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

On Saturday, US Air Force B-1B Lancer bombers escorted by fighters flew in international airspace over waters east of North Korea in a show of force after a heated exchange of rhetoric between Trump and Kim over North Korea’s nuclear and missile programs.

The Pentagon said the flight was the farthest north of the demilitarised zone separating North and South Korea that any U.S. fighter jet or bomber has flown in the 21st century.

“That operation was conducted in international airspace, over international waters, so we have the right to fly, sail and operate where legally permissible around the globe,” Pentagon spokesman Colonel Robert Manning said.

North Korea, which has remained technically at war with the United States since the 1950 to 1953 Korean War ended in a truce and not a peace treaty, has been working to develop nuclear-tipped missiles capable of hitting the US mainland and conducted its sixth and largest nuclear test this month.

Pyongyang accuses the United States, which has 28,500 troops in South Korea, of planning to invade and regularly threatens to destroy it and its Asian allies.

However, the recent spike in rhetoric from both sides has fuelled tensions and raised fears of miscalculation by one side or the other that could have massive repercussions.

The Pentagon said the bomber flight indicated the range of military options available to Trump, but US officials have repeatedly stressed that despite the war of words, the administration prefers a negotiated solution to the crisis.

The latest round of heavy verbal salvoes began when Mr Trump threatened in his maiden UN address last Tuesday to “totally destroy” North Korea, a country of 26 million people, if it threatened the United States or its allies.

In an unprecedented direct statement on Friday, Mr Kim responded by calling Mr Trump a “mentally deranged US dotard” whom he would tame with fire.

Mr Kim said North Korea would consider the “highest level of hard-line countermeasure in history” against the United States and that Trump’s comments had confirmed Pyongyang’s nuclear programme was “the correct path”.

Mr Ri told the UN General Assembly on Saturday that targeting the US mainland with its rockets was inevitable after “Mr Evil President” Trump called Kim a “rocket man” on a suicide mission.

On Twitter late Saturday, Mr Trump replied: “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!”

On Monday, North Korea, which has pursued its missile and nuclear programmes in defiance of international sanctions, said it “bitterly condemned the reckless remarks” of Trump.

United Nations Secretary-General Antonio Guterres said on Monday that the only solution to the crisis was a political one.

“Fiery talk can lead to fatal misunderstandings,” UN spokesman Stephane Dujarric said.