UNITED NATIONS (REUTERS) - Russia sent home nearly two-thirds of some 30,000 North Koreans working there during 2018 and China repatriated more than half, but did not specify a figure, according to unpublished reports by Moscow and Beijing to the United Nations Security Council.

The one-page reports, seen by Reuters on Tuesday (March 26), were submitted to the council's North Korea sanctions committee in compliance with a 2017 resolution that demanded the repatriation of all North Korean workers by the end of this year to stop them earning foreign currency for leader Kim Jong Un's authorities.

The United States has said it believed Pyongyang was earning more than US$500 million (S$675 million) a year from nearly 100,000 workers abroad, of which some 80,000 were in China and 30,000 in Russia.

The UN Security Council has steadily toughened sanctions on North Korea since 2006 to choke off funding for Pyongyang's nuclear and ballistic missile programmes.

US President Donald Trump and North Korean leader Kim Jong Un have met twice in the past year in a bid to negotiate denuclearisation.

The December 2017 UN resolution required countries to report to the sanctions committee this month on all North Korean workers repatriated during 2018, "including an explanation of why less than half of such" workers were repatriated, if applicable.

Russia reported that in 2018, the number of North Koreans "with valid work permits in the Russian Federation decreased from 30,023 to 11,490 persons".

Key North Korean ally China said it had repatriated "more than half of the total DPRK (North Korea) nationals earning income".

"China will continue earnestly implementing its international obligations, carry out the repatriation work in an orderly manner and complete the repatriation on time," wrote China's mission to the United Nations, adding that it did not want the report to be made public.

In 2015, UN human rights investigator Marzuki Darusman said that the North Koreans abroad worked mainly in mining, logging, textile and construction.

The reports submitted by Russia and China to the sanctions committee did not specify what industries had employed the North Koreans.

New York-based Human Rights Watch said in a 2017 report that "the treatment of North Korean workers overseas falls short of international labour standards, with no right to freedom of association or expression, control by minders who limit freedom of movement and access to information from the outside world, long working hours and no right to refuse overtime".

North Korea has said its labourers were working abroad legally and were not mistreated or forced to go.