A special United Nations investigator appointed to examine human rights abuses in North Korea expressed deep concern on Wednesday about what he described as the country’s systematic deployment of workers overseas for what amounts to forced labor.

The investigator, Marzuki Darusman, an Indonesian lawyer and former attorney general appointed to his post by the United Nations Human Rights Council in 2010, said in his latest assessment that more than 50,000 North Korean workers are now toiling abroad, mainly in China and Russia but also in at least 15 other countries in Africa, the Middle East and South Asia. They work in the construction, mining, logging and textile industries.

Mr. Darusman said much of their earnings were taken by the North Korean government, which is in severe need of foreign currency because of international sanctions that restrict its financial activities. He added that North Korea made $1.2 billion to $2.3 billion a year from these workers, who do not know the details of their employment contracts, are under constant surveillance by North Korean security personnel and are sometimes required to work 20 hours a day, with only one or two rest days a month.