Also penned by the UK, France and Germany, the letter was sent on June 29, the day Trump tweeted that he wanted to shake hands with Kim Jong-un during his visit to the Korean peninsula. The world of North Korean laborers abroad is indeed a shadowy one and the UN estimates that thousands of them are sent to different countries every year to generate hard currency for the regime in Pyongyang. The website "North Korea in the World" which is run by the East-West Center and the National Committee on North Korea, maintains statistics about the countries believed to be currently hosting or that have recently hosted North Korean workers.

The vast majority of them are known to go to China and Russia where they are employed in construction, agriculture, logging, garment work and traditional medicine. A smaller number work in North Korean restaurants abroad and they made headlines in 2016 when 13 workers defected to South Korea. Even though China and Russia are believed to host an estimated (upper estimate) 80,000 and 40,000 North Korean laborers respectively, they are thought to be present (or were recently present) in at least 41 countries.