"I trust him, but he clearly likes to launch rockets and that's why I call him 'rocket man'," Trump said in London where the NATO summit is inaugurated on December 3.
Despite the words of "trust," the US president does not rule out the use of military force against North Korea if necessary.
"If military force is needed, we will use it," Trump said.
Since 2018, the leaders of the US and North Korea, Donald Trump and Kim Jong-un, have held three meetings in which they agreed to move towards the denuclearization of the peninsula and the normalization of relations.
Three inter-Korean summits were also held last year.
However, the process of distention in Korea and the negotiations between Pyongyang and Washington to denuclearize the peninsula have been stalled in recent months.
Last May Pyongyang resumed arms testing, after a 17-month break.
The previous test took place last October 31, when North Korea fired two projectiles from a multiple rocket launcher in the direction of the East Sea, also known as the Sea of Japan.