The treaty prompted a protest from the United Nations' Special Rapporteur on Human Rights in North Korea, Marzuki Darusman, who said he feared for those who might be forcibly repatriated. Concerned about North Korea-Russia agreement: Special Rapporteur Marzuki Darusman Credit:UN "In fact," he continued, "the practice of sending workers abroad to be exploited may constitute state-sponsored enslavement of human beings, possibly amounting to a specific category of crime against humanity." It is a win-win trade for the two states, as drought-hit North Korea needs money for its nuclear program while cheap labour does not go amiss in Russia as it sinks deeper into economic crisis. But for the workers being outsourced, it is a dismal life in an archipelago of Siberian labour camps or on building sites, where they are watched by "political cadres", fed a starvation diet and paid only a fraction of their wages. "These workers face threats of government reprisals against them or their relatives in North Korea if they attempt to escape or complain to outside parties," the US State Department said recently. "Workers' salaries are deposited into accounts controlled by the North Korean government, which keeps most of the money, claiming various 'voluntary' contributions to government endeavours."

North Korea is believed to earn some $US2 billion ($2.8 billion) a year from sending tens of thousands of workers abroad, not only to Russia but also to China and Mongolia. The number of workers in Russia is said to be about 25,000. It's unclear whether recent sanctions against North Korea could affect these transactions. The gate of a North Korean timber camp in Siberia. Credit:Vice/Jason Mojica Few Western journalists have seen the North Korean work camps, deep in the forests in remote parts of Siberia, but the Canadian founder of Vice News, Shane Smith, and the Russian reporter, Simon Ostrovsky, did manage to film the secret logging on a trip to the Amur region in 2011. Travelling for hours on trains through the taiga, they found North Korean-run villages, with North Korean propaganda slogans and North Korean music so that, as Smith put it, "you never lose the North Korean experience". The Amur River. Credit:WikiCommons

On returning home at the end of their contracts, the North Korean labourers had to undergo "reintegration" to catch up on any propaganda they might have missed, the reporters said. An investigation by Canada's Globe and Mail newspaper discovered that North Korean builders had been used to renovate infrastructure in Vladivostok for the 2012 Asia-Pacific Economic Co-operation (APEC) summit, although the workers were out of sight by the time the summit took place. North Korean leader Kim Jong-il with Russian President Dmitry Medvedev, right, meet in the Russian Far East, outside Ulan-Ude, in 2011. Credit:AP Russian foremen were said to prefer North Korean labourers to guest workers from Central Asia because the former always had visas while the latter could be illegal. "The North Koreans are seen as the best foreign workers," Professor Alexander Latkin, of Vladivostok University, said. "They work intensely from morning until night. They don't require high payment, or demand decent food or living conditions. It's a form of slavery."

North Korea's arms: a matter of international concern. A South Korean anti-war protester. Credit:AP Co-operation with North Korea goes back to Soviet times. Kim Jong-un's father, Kim Jong-il, was born in Russia while his father, Kim Il-sung, was being trained in Moscow for the North Korean leadership. The labour trade with North Korea dates to the Brezhnev era. In the 1990s, under Boris Yeltsin, North Korean workers began defecting to Russia and the then-liberal Russian authorities were sufficiently embarrassed by the situation to make it known they would not be averse to the South Koreans helping defectors. In 1994, The Independent interviewed a runaway in Moscow and spoke of 170 such cases. But by 2011, the Vice News team, who were not allowed into any of the North Korean camps but filmed workers only in the forests, found an atmosphere of control and fear. The reporters were questioned by the FSB at the end of their trip, which coincided with an unpublicised visit to Siberia by the then North Korean leader Kim Jong-il and the then Russian President Dmitry Medvedev.

"When we found out that Kim Jong-il was in the region, making deals for even more of these types of labour arrangements, we knew we had to show what was going on," Smith said. "A dictator trying to sell more of his people, to make more money, to build more nuclear weapons that he can use to blackmail the West into giving North Korea more aid, thus enabling him to maintain his regime." Follow FairfaxForeign on Twitter Follow FairfaxForeign on Facebook