North Korea said on Tuesday it has sent labourers to work abroad legally in Russia, China and elsewhere and that it was a "vicious slander" to say they were mistreated or forced to go.

UN human rights investigator Marzuki Darusman last month raised concerns that North Korea (DPRK) has forced some 50,000 people to work abroad "under overall conditions that reportedly amount to forced labour." He urged countries where they have been sent to grant him access to investigate.

"They are saying thousands of DPRK laborers are under harsh treatment and they are engaged in forced labour," Ri Hung Sik, ambassador-at-large for the North Korean Foreign Ministry, said at a news conference in New York.

"This is totally false. This is fabricated," he said. "This is vicious slander towards my republic."

Ri said North Koreans were working in countries like Russia, China, Kuwait and Angola, but could not say how many were working abroad. "We have our labourers working in foreign countries under legal contract," he said.

Darusman told the UN General Assembly committee last month that the labourers were sent abroad to circumvent sanctions and earn foreign currency that amounted to between $1.2 billion and $2.3 billion annually.

The committee is expected to vote this week on a resolution drafted by the European Union and Japan that would condemn human rights abuses in North Korea.

The vote is an annual occurrence, but Ri urged the European Union and Japan to withdraw their draft resolution and "remedy their own shortcomings and reflect on their dire human rights situations before they criticise others."

The UN Security Council also added the issue of human rights in North Korea to its agenda in December, after a UN Commission of Inquiry report detailed abuses in the impoverished country that were comparable to Nazi-era atrocities.

"It is not an organ to deal with human rights issues," Ri said of the Security Council.

North Korea is under UN sanctions for carrying out nuclear tests and missile launches. In addition to an arms embargo, Pyongyang is banned from trading in nuclear and missile technology and is not allowed to import luxury goods.