North Korea accused the US of creating a situation in which “a thermonuclear war may break out at any moment”, as hundreds of American troops began 11 days of joint military exercises with its southern neighbour.
Roughly 1,000 American service members and about 500 South Korean troops will carry out Operation Max Thunder, a training exercise involving aircraft carriers, fighter jets and military drills.
The Trump administration has stressed it is a routine drill, planned months ago.
However, North Korea said that the presence of US troops in the Korean peninsula had created a situation in which “a thermonuclear war may break out at any moment.
Kim In-Ryong, the country’s ambassador the the UN, said Pyongyang was “ready to react to any mode of war desired to the US.”
North Korea will continue to test missiles frequently, despite escalating tensions with the US, according to the secretive communist state's Foreign Ministry.
“We'll be conducting more missile tests on a weekly, monthly and yearly basis,” Vice Foreign Minister Han Song-Ryol said.
Their comments came after the US Vice President, Mike Pence declared earlier this week that “the time for failed dialogue” was over.
“As the President says, it’s time for them to behave, to listen to the world community and to set aside their nuclear ambitions, their ballistic missile ambitions, and be willing to join the family of nations,” Mr Pence told CNN.
Mr Pence made the statement after talks in Tokyo with the Japanese Prime Minister Shinzo Abe.
The delegations from both countries agreed that they needed to persuade China to work more closely with them to deal with North Korean aggression, and use its “extraordinary levers” to pressure Pyongyang to abandon its weapons programme.
China is one of North Korea’s largest trade partners, and the international community has called for multilateral economic sanctions against the regime.
Beijing was forced to defend its continued trade with North Korea after Chinese-made trucks were used to display missiles in a Pyongyang military parade.
"China has been performing its international obligations strictly, including those stipulated in the Security Council resolution,” a spokesperson for the Chinese government told the Associated Press.
“But meanwhile, we carry on normal economic exchanges and trade with all parties including North Korea."
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