Human rights groups are pressing Russia to give access to labour camps in Siberia, after reports that they continue to operate, seven years after they were supposed to have closed.
Labour camps - the infamous gulags where millions of prisoners toiled and perished - were supposedly shut with the demise of the Soviet Union.
But reports in the Moscow press quoting officials from the Economic Development and Trade Ministry say the practice continues - with thousands of North Koreans working in grim conditions for almost no pay so that their country can pay off its $5.5 billion debt to Russia.
"We need access, definitely, definitely," said Mr Alexander Petrov of the US-funded Human Rights Watch. "Nobody has ever been there." The issue has surfaced with the arrival in Moscow of the North Korean leader, Mr Kim Jong-il, who this weekend pledged to pay off debts in exchange for Russian assistance to rebuild his country.
There was immediate speculation that, with North Korea bankrupt, Mr Kim would revive the practice, begun in the 1960s, in which tens of thousands of labourers are sent to Russia to toil in the forests. These camps were supposedly closed after the agreement between the two nations ended in 1993.
But far from being closed, these camps are likely to be expanded as North Korea exports more workers to pay for additional economic assistance including the building of a nuclear power station.
An anonymous Moscow official was quoted as telling the Moscow Times: "North Korean labour holds the position of a special type of mass quantity product. Workers are working unpaid or for an insignificant salary." The official said that in return for the labour, Russia cuts $50 million per year off North Korea's debt.
There are fears that conditions remain the same as in the early 1990s, when an Amnesty International report spoke of barbarous conditions for 30,000 North Koreans, who lived in barracks in the camps with armed guards to prevent escapes.
Russia's authorities have been silent on the issue, but there is concern that the country may be breaking the terms of human rights and anti-slavery conventions.
"It is hard to say whether the work in the camps can be qualified as slavery," said Ms Rachel Denber, deputy director of Human Rights Watch. "But we do know that Russian police are involved in guaranteeing security for those timber camps where the North Koreans are meant to stay. That means that there is an obvious element of compulsion involved."
Questioning Mr Kim on the issue yesterday was not possible because he gives no press conferences and Western photographers are barred from taking his photograph.