In the letter dated July 6, Kim thanked Trump for his "energetic and extraordinary efforts" to improve the once hostile relations between the two countries.
North Korean officials did not turn up to a Thursday meeting with the US military about repatriating the remains of American war dead, according to a USA official with knowledge of the situation.
Under the latest sanctions resolution adopted in December, crude oil supplies to North Korea were capped at four million barrels per year and a ceiling of 500,000 barrels of refined oil products per year was set.
In another development on Thursday, North Korean officials failed to turn up for talks with a U.S. team on the repatriation of the remains of American soldiers killed in the 1950-53 Korean war. Recent reports suggest that the North has continued to expand infrastructure at nuclear and missile sites and that USA intelligence assesses that the North does not intend to fully denuclearize.
Coming after a year of Twitter taunts and nuclear brinkmanship, the meeting between Kim and Trump was historic, in that it was the first meeting between a USA president and his North Korean counterpart.
Mr. Pompeo denied that the talks went poorly, telling pool reporters that progress was made "in every element of our discussions". Reports say North Korea is now asking for higher-level talks for Sunday.
But there's growing skepticism in Washington over the Trump administration's engagement with North Korea. The charge of a sanctions breach comes as Washington engages North Korea in a bid to convince Pyongyang to give up its nuclear weapons.
It was not immediately clear why North Korean officials had not attended the meeting or whether they had ever confirmed their intention to.
The Defense Department estimates there are up to 5,300 sets of USA service member remains still somewhere in North Korea.
There were reports that North Korea had, rather than dismantled its nuclear programme, satellite images showed that it was actually upgrading its nuclear facilities.
"We will be ready", USA state department spokeswoman Heather Nauert said.
Mr Pompeo traveled to Pyongyang for two days last week in a bid to flesh out denuclearisation commitments made during last month's historic summit. Despite the "Hail Mary" nature of the summit, denuclearization talks with North Korea made halting progress one yard at a time.
There was no call or explanation from North Korean officials on why they skipped the meeting.