A North Korean activist who was imprisoned in China for helping North Korean refugees has been freed, reported a Christian human rights group Monday.

Yoo Sang-joon is now safely in South Korea after spending the last four months in a prison located in northern China, according to Christian Solidarity Worldwide (CSW). He is said to have endured extreme cold during his imprisonment and was believed he would die while being confined in China.

Although he was sent winter clothes early in his prison term, he was only given them on the day of his release. Yoo reportedly still suffers from a number of physical problems as a result of his incarceration.

“I am grateful from the depths of my heart to CSW and CSW supporters for all the deep concern, prayer and advocacy on my behalf while I was in prison,” said Yoo, according to CSW.

Yoo, a North Korean survivor, was arrested near the Chinese-Mongolian border while trying to rescue other North Koreans from danger in China. He had lost his wife and youngest son in the North Korean famine. He realized the same fate awaited him and his remaining son if they remained in the country, and decided to flee to China.

But unable to travel together, his 10-year-old son, Chul Min, attempted to cross the Mongolian border by himself. Unfamiliar with the inhospitable terrain, he wandered 26 hours and – suffering from dehydration and weakened from the famine – died before crossing the border.

Yoo himself was able to reach South Korea and is a citizen, but he continues to be haunted by the loss of his family. As a result, he has dedicated his life to helping North Korean refugees in China, especially children, at the risk of his own safety.

South Korean activists consider Yoo’s case unique because of his tragic personal story.

It is said that at least 500,000 North Koreans have crossed the border over to China in the past 10 years. North Koreans who flee to China are considered “refugees” deserving of protection by the U.N. Special Rapporteur on North Korea, but China has claimed they are “economic migrants” and not refugees.

China has used the status as an excuse to return North Korean refugees back to their country where they face imprisonment, torture, and sometimes execution for leaving the country – a state crime.

North Korea is one of the most repressive regimes in the world and is ranked by the watchdog Open Doors as the world’s worst persecutor of Christians. Citizens of the communist state are forced to adhere to a personality cult that revolves around worshipping current dictator Kim Jong Il and his deceased father, Kim Il Sung.

In the face of these grave consequences, Yoo’s punishment is considered light.

“The fact that Yoo Sang-joon was released after only four months, in contrast to other activists who have served up to and surpassing four years, is surely a testament to your prayers, network and fervent advocacy,” said a CSW contact on the ground in Asia (location cannot be identified for security reason). “We thank you all so very much!”