The US and South Korea will go ahead with joint military drills next week, resisting pressure from North Korea and its ally China to halt the contentious exercises.
North Korea's rapid progress in developing nuclear weapons and missiles capable of reaching the US mainland has fuelled a rise in tensions in recent months.
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US President Donald Trump warned North Korea last week it would face "fire and fury" if it threatened the United States, prompting North Korea to say it was considering plans to fire missiles at the US Pacific territory of Guam.
Annual military drills involving tens of thousands of US and South Korean troops are due to begin on Monday.
China, North Korea's main ally and trading partner, has urged the United States and South Korea to scrap the drills in exchange for North Korea calling a halt to its weapons programs.
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Joseph Dunford, Chairman of the US Joint Chiefs of Staff, said the exercises were "not currently on the table as part of the negotiation at any level".
"My advice to our leadership is that we not dial back our exercises. The exercises are very important to maintaining the ability of the alliance to defend itself," Dunford told reporters in Beijing after meeting his Chinese counterparts.
"As long as the threat in North Korea exists, we need to maintain a high state of readiness to respond to that threat," he said.