The letter "was flown to Pyongyang and delivered by hand" over the weekend, reported CNN citing an anonymous source. It has also been reported that Kim Yong-chol, Vice Chairman of North Korea’s ruling Workers' Party, may meet US Secretary of State Mike Pompeo later this week in Washington to work on details of the expected second Trump-Kim meeting.

The two leaders had their first summit in Singapore in June, where they agreed to act for the denuclearization on the Korean Peninsula in exchange for security guarantees from the US. There has been no more significant progress since then.