The note, written by North Korean leader Kim Jong-un on July 6, was shared on Twitter by Trump, who deemed it 'nice', adding that 'great progress being made'.

Trump had met Kim in Singapore on June 12, writing his name in history by becoming the first sitting US President to meet a North Korean leader in person. 

It was there that the two leaders has pledged to denuclearise the Korean Peninsula.

In his note, Kim said that he hopes 'the invariable trust and confidence' in Trump 'will 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."

Meanwhile, in just the latest sign of difficulty, a UN Security Council diplomat told CNN on Thursday that the US submitted a report to the United Nations North Korea Security Council Sanctions Committee, charging North Korea with evading UN sanctions through illegal transfers of refined petroleum at sea.

"In a letter Wednesday to the UN, the US asks the world body to call on all members to 'exercise enhanced vigilance' against North Korean attempts to procure more petroleum supplies," reported CNN.

Image: Donald Trump/Twitter