Thousands of North Koreans are being sent to work in slave-like conditions in Russia to fill a huge labour shortage exacerbated by Russia's ongoing invasion of Ukraine, the BBC has learned.

Moscow has repeatedly turned to Pyongyang to help it fight the war, using its missiles, artillery shells and its soldiers.

Now, with many of Russia's men either killed or tied up fighting - or having fled the country - South Korean intelligence officials have told the BBC that Moscow is increasingly relying on North Korean labourers.

We interviewed six North Korean workers who have fled Russia since the start of the war, along with South Korean government officials, researchers and those helping to rescue the labourers.

They detailed how the men are subjected to "abysmal" working conditions, and how the North Korean authorities are tightening their control over the workers to stop them escaping.

One of the workers, Jin, told the BBC that when he landed in Russia's Far East, he was chaperoned from the airport to a construction site by a North Korean security agent, who ordered him not to talk to anyone or look at anything.

"The outside world is our enemy," the agent told him. He was put straight to work building high-rise apartment blocks for more than 18 hours a day, he said.

All six workers we spoke to described the same punishing workdays – waking at 6am and being forced to build high-rise apartments until 2am the next morning, with just two days off a year.

We have changed their names to protect them.

"Waking up was terrifying, realising you had to repeat the same day over again," said another construction worker, Tae, who managed to escape Russia last year. Tae recalled how his hands would seize up in the morning, unable to open, paralysed from the previous day's work.

"Some people would leave their post to sleep in the day, or fall asleep standing up, but the supervisors would find them and beat them. It was truly like we were dying," said another of the workers, Chan.

"The conditions are truly abysmal," said Kang Dong-wan, a professor at South Korea's Dong-A University who has travelled to Russia multiple times to interview North Korean labourers.

"The workers are exposed to very dangerous situations. At night the lights........

© BBC