Jeremy Corbyn has called on US president Donald Trump and North Korean leader Kim Jong Un to "wind down the war of rhetoric".
The world leaders have been engaged in a war of words, with Mr Trump threatening to rain "fire and fury" on the communist state after Pyongyang said it was "carefully examining" a plan to hit Guam with missiles.
Prime Minister Theresa May has been urged by Mr Corbyn not to commit any of Britain's armed forces to military action in the Korea crisis.
Writing in the Sunday Mirror, Labour leader Mr Corbyn said: "Trump and Kim must immediately wind down the war of rhetoric, as the German chancellor Angela Merkel has demanded.
"The risks of an unintended escalation into full-blown conflict are too great for the whole world.
"We cannot play fast and loose with nuclear weapons and nuclear threats. Our government must press for measured responses to bring the temperature down.
"Our government must not drag our country into any military action over the Korea crisis, including joint exercises.
"There can be no question of blind loyalty to the erratic and belligerent Trump administration.
"US-led regime-change wars and the threat of more to come have made this crisis more dangerous and difficult to resolve."
He said any future Labour government would be committed to remove nuclear weapons from the world and "global pressure for dialogue and diplomacy must be overwhelming".