"I think it's exactly where we were a year ago", said Darcie Draudt, a North Korea researcher and visiting scholar at Seoul's Yonsei University.
The timing of the letter is key, explained two sources, who said that Kim planned the delivery before the anniversary of the leaders' first meeting to allow Trump to tout continued success.
Trump, who has described previous correspondence from Kim as "beautiful letters", said the most recent one was a "very warm, very nice letter". "I wouldn't let that happen", Trump told reporters.
The CIA operatives had met with Kim, 45, on several occasions, according to a Wall Street Journal report.
Trump was scheduled to visit Japan and South Korea later this month to discuss the denuclearization of the peninsula, according to the U.S. State Department.
Trump said talks between USA and North Korean nuclear negotiators need to advance before another meeting.
The United States and some two dozen countries asked the Security Council sanctions committee to demand an immediate halt to deliveries of refined petroleum to North Korea.
Thousands Of Hong Kong Protesters Take To Streets To Protest Extradition Bill
But in recent years, Hong Kong's pro-Beijing leaders have taken a harder line and resisted protester demands. The demonstrations in Hong Kong are not over.
Susan Rice, who was national security adviser for Trump's Democratic predecessor, Barack Obama, tweeted her reaction: "America, this tells you all you need to know about our so-called 'Commander-in-Chief'".
As he was waiting for a flight to Macau at Kuala Lumpur International Airport in February 2017, two women smeared the nerve agent on his face, resulting in his death.
The latest US allegation comes after a report by a UN Panel of Experts submitted to the council earlier this year that said North Korea successfully evaded sanctions to import as much as seven-and-a-half times the allowed amount of refined petroleum last year.
The agreement signed by Kim and Trump in Singapore "is in danger of being a blank sheet of paper because the U.S.is turning a blind eye to its implementation", KCNA said.
On the one-year anniversary of the historic Singapore summit between the leaders of North Korea and the US,.
FILE PHOTO: U.S. President Donald Trump shakes hands with North Korean leader Kim Jong Un at the Capella Hotel on Sentosa island in Singapore June 12, 2018.
But there has been little progress since then and tension has again been rising with North Korea resuming some limited testing of weapons and warning of "truly undesired consequences" if the United States was not more flexible.
A feature on the murder in the Japanese newspaper, the Asahi Shimbun, in March this year, noted that a Malaysian investigation has discovered about $US124,000 in cash in Kim Jong-nam's travel bag.