US President Donald Trump on Thursday said North Korean leader Kim Jong Un sent him a “very nice note” on future relations between the United States and North Korea, days after the Hermit Kingdom slammed “regrettable” talks with Secretary of State Mike Pompeo’s delegation.

In his letter, which was written 24 days after the June 12 summit in Singapore, Kim addressed Mr Trump as "Your Excellency Mr President".

He wrote: "I deeply appreciate the energetic and extraordinary efforts made by Your Excellency Mr. President for the improvement of relations between the two countries and the faithful implementation of the joint statement," the letter read, referring to an agreement the two leaders signed at their summit in Singapore last month.

I firmly believe that the strong will, sincere efforts and unique approach of myself and Your Excellency Mr. President aimed at opening up a new future between the DPRK and the U.S. will surely come to fruition," it added, using the acronym for North Korea's official name, the Democratic People's Republic of Korea.

Wishing that the invariable trust and confidence in Your Excellency Mr. President will be further strengthened in the future process of taking practical actions, I extend my conviction that the epochal progress in promoting the DPRK-U.S. relations will bring our next meeting forward."