US President Donald Trump has declared war on North Korea, Pyongyang says, adding that it reserves the right to take countermeasures, including shooting down US bombers even if they are not in its air space.

Key points: North Korea says it is yet to be seen which country will be totally destroyed

North Korea says it is yet to be seen which country will be totally destroyed The Pentagon responds that it will provide Mr Trump with military "options"

The Pentagon responds that it will provide Mr Trump with military "options" China calls for immediate calm in highly complex, sensitive situation

"The whole world should clearly remember it was the US who first declared war on our country," Foreign Minister Ri Yong Ho told reporters in New York.

"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 in a direct reference to a tweet by Mr Trump on Saturday.

Sorry, this video has expired Suggestion US declared war on North Korea 'absurd,' White House says

In response, the Pentagon said it would be providing Mr Trump with "options" on how to deal with Pyongyang.

"If North Korea does not stop their provocative actions, you know, we will make sure that we provide options to the President to deal with North Korea," Pentagon spokesman Colonel Robert Manning said.

White House spokeswoman Sarah Saunders later denied the accusation that Mr Trump had declared war on North Korea, and called the suggestion "absurd".

The increasingly heated rhetoric between Mr Trump and North Korean leader Kim Jong-un is raising fears of a risk of a miscalculation by one side or the other that could have massive repercussions.

On Monday, China called for all sides in the North Korea missile crisis to show restraint adding that the situation was "getting too dangerous".

Australia's Foreign Minister Julie Bishop said she believes war with North Korea can be avoided.

"I believe that North Korea can be deterred, I don't think there's anything inevitable about this current circumstance," she said.

"Obviously if North Korea were to follow through on its rhetoric and attack there would be a retaliation, the consequences would be obvious."

Trump's words an 'intolerable insult to the Korean people'

Over the weekend, Mr Ri told the UN General Assembly that targeting the US mainland with its rockets was inevitable after "Mr Evil President" called the North Korean leader a "rocket man on a suicide mission".

Sorry, this video has expired North Korean Foreign Minister Ri Yong-ho addresses the UN General Assembly (Image: Reuters)

"Just heard Foreign Minister of North Korea speak at UN. If he echoes thoughts of Little Rocket Man, they won't be around much longer!" Mr Trump said on Twitter on Saturday.

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North Korea, which has pursued its missile and nuclear programs in defiance of international condemnation and economic sanctions, said it "bitterly condemned the reckless remarks" of Mr Trump.

They were an "intolerable insult to the Korean people" and a declaration of war, the North's official news agency said on Monday.

Pyongyang accuses the United States, which has 28,500 troops in South Korea, a legacy of the 1950-1953 Korean war, of planning to invade and regularly threatens to destroy it and its Asian allies.

The United States and South Korea are technically still at war with North Korea because the 1950s conflict ended with a truce, not a peace treaty.

'It's getting too dangerous, and in nobody's interest': China

Asked how concerned China was the war of words between Mr Trump and North Korea could get out of control, Beijing's UN ambassador Liu Jieyi told reporters that the current situation was getting out of hand and that negotiations could be the only way forward.

"We want things to calm down. It's getting too dangerous and it's in nobody's interest," Mr Liu said.

"We certainly hope that [the United States and North Korea] will see that there is no other way than negotiations to solve the nuclear issue on the Korean Peninsula.

"The alternative is a disaster."

Meanwhile, Foreign Ministry spokesman Lu Kang described the situation as highly complex and sensitive.

Mr Lu said it was vitally important everyone strictly, fully and correctly implemented all North Korea related UN resolutions, which call for both tighter sanctions and efforts to resume dialogue.

"[All sides should] not further irritate each other and add oil to the flames of the tense situation on the peninsula at present," Mr Lu told a daily news briefing.

"We hope all sides do not continue doing things to irritate each other and should instead exercise restraint."

Reuters