North Korean workers are being given a methamphetamine-based drug in the hope it will speed up a major construction project, according to reports.
Project managers in the city's capital of Pyongyang are said to be under so much pressure to finish the job on time that they have resorted to openly providing builders with the drug.
Nicknamed "ice," it is a form of the powerful stimulant methamphetamine, which is also known as crystal meth.
When snorted or inhaled, crystal meth gives users a sense of euphoria, increased energy levels and a suppressed appetite. The effects can last up to 12 hours.
Hundreds of thousands of North Korean citizens have been roped in to finish the project, which consists of a 70-floor skyscraper and more than 60 apartment blocks.
It was approved earlier this year by North Korean leader Kim Jong-un in defiance of tough sanctions placed on the hermit state over its nuclear weapons tests.
"Project managers are now openly providing drugs to construction workers so that they will work faster," a construction source in Pyongyang told Radio Free Asia.
"[They] are undergoing terrible sufferings in their work."
Human rights workers in Asia said the working conditions amounted to slave labour and urged the UN to take further action against Kim Jong-un.
Phil Robertson, Asia director for Human Rights Watch, said: "It's going to be hard to verify that this is happening, but if it is confirmed then we utterly condemned it.
"The real issue here is slave labour, and our immediate reaction to this was that if they want faster workers why not actually pay them, instead of resorting to giving them drugs?
"The North Korean government wants to finish these buildings to somehow prove that they are a developed country. But this kind of forced labour has been unilaterally condemned by the international community."
Mr Robertson added: "It is a throwback to the Second World War when governments regularly resorted to forcing labour of their citizens."
North Korea has been producing methamphetamine to increase its funds since the 1970s.
It was was initially sold as a medicine, but quickly became a hugely popular drug.
It is produced in state-run facilities by underpaid chemists and sold both domestically and internationally.
As the production and sale of opium declined in the early 2000s, methamphetamine became even more widespread.