This is the latest in an exchange of insults between the two leaders.

United States President Donald Trump on Friday warned North Korean leader Kim Jong Un that he would be “tested” like never before.

This is the latest in an exchange of insults between the two leaders.

“Kim Jong Un of North Korea, who is obviously a madman who doesn’t mind starving or killing his people, will be tested like never before!” Mr. Trump tweeted.

Earlier in the day, Mr. Kim blasted Mr. Trump as a “mentally deranged US dotard”, who will “pay dearly” for threatening to destroy North Korea.

Mr. Trump “insulted me and my country in front of the eyes of the world and made the most ferocious declaration of a war in history,” Mr. Kim said, according to the official Korean Central News Agency. He blasted Mr. Trump’s maiden speech to the U.N. General Assembly as “unprecedented rude nonsense”.

Mr. Trump branded Mr. Kim “Rocket Man” and threatened to “totally destroy North Korea” in his U.N. speech. Washington followed by announcing tougher sanctions on North Korea on Thursday.

Mr. Trump has earlier threatened Pyongyang with “fire and fury”.

Mr. Trump has traded tough rhetoric with North Korea as it pushed an increasingly brazen weapons programme in recent months, with missile launches and its sixth and largest nuclear test.

On the fringes of the U.N. General Assembly, North Korean Foreign Minister Ri Yong-ho told reporters that Pyongyang might now consider detonating a hydrogen bomb outside its territory.