Moscow:  Russian Foreign Minister Sergei Lavrov has likened the war of words between US President Donald Trump and North Korean leader Kim Jong-un to a kindergarten fight between children.

The North Korean leader earlier labelled Trump "mentally deranged" and a "dotard" after Trump threatened to destroy his country.

Trump responded with a tweet calling Kim Jong-un "a madman" who "will be tested like never before!"

Lavrov said a pause was needed, "to calm down the hotheads", BBC reported on Friday.

"Yes, it's unacceptable to silently watch North Korea's nuclear military adventures but it is also unacceptable to unleash war on the Korean Peninsula," he said.

He called for a political process, which he said was a key part of the United Nations Security Council process.

"Together with China we'll continue to strive for a reasonable approach and not an emotional one like when children in a kindergarten start fighting and no-one can stop them," he said.

The North Korean leader had attacked Donald Trump days after his speech at the UN, in which the US president said he would "totally destroy" North Korea if the US was forced to defend itself or its allies.

He also mocked Kim Jong-un with a disparaging nickname, saying: "Rocket man is on a suicide mission."

But the North Korean leader said remarks by the "deranged" US President convinced him he is right to develop weapons for North Korea.

In an unprecedented personal statement, Kim said Trump would "pay dearly" for his speech, which he labelled "unprecedented rude nonsense".

He said Trump had insulted his country in the eyes of the world, and threatened to "surely and definitely tame the mentally deranged US dotard with fire."

Experts say this is the first time a North Korean leader has made a direct address to an international audience - and it merits serious and thorough consideration.

China also urged a calming of the heated rhetoric on both sides, saying the issue was "complicated and sensitive".

"All relevant parties should exercise restraint instead of provoking each other," said Foreign Minister spokesman Lu Kang.