SEOUL, South Korea - When Lee Oui-ryok was accepted as a 17-year-old into North Korea's August 28 work brigade in early 2006, his orphanage celebrated with flowers, speeches and cheers.

This is a chance at redemption, he thought. His father had been sent to a prison camp and his mother had fled the country when he was 8.

Lee saw the work brigade as a path toward possible membership in the Workers' Party one day and restoring his name in the eyes of North Korea's leadership.

That dream was soon forgotten. Lee said he endured endless hours of backbreaking labor seven days a week - constantly hungry and impossibly exhausted - constructing apartment buildings in Pyongyang for the elite. He saw a colleague plunge to his death, and others deliberately injured themselves to be excused from work.

North Korea's economy - and construction industry, in particular - is built on slave labor. For decades, hundreds of thousands of men, women and children are dragooned into dolgyeokdae, literally "stormtrooper," work crews for little or no pay, barely fed enough to survive and often forced to sleep in makeshift housing they built themselves, according to rights groups and reports by the State Departmentand others.

Today, South Korean President Moon Jae-in is talking boldly of building road and railway links inside North Korea as a first step toward European Union-style regional economic integration.

In September, Moon took his country's business elite, including the head of the national railway company, to Pyongyang to persuade North Korean leader Kim Jong Un that the South was ready to invest as soon as U.N. sanctions are lifted.

But human rights activists are asking: Could Moon's ambitious plans help undermine North Korea's entrenched system of forced labor? Or will they inadvertently fuel and encourage that system?

"The South Korean government and companies chomping at the bit to get into North Korea need to consider the kind of reputational damage they will suffer if it's found their investments are being supported by forced labor," wrote Phil Robertson, deputy director of Human Rights Watch's Asia division. "South Korea has so far been shamefully negligent in doing real due diligence on labor rights grounds for proposed projects in North Korea."

The brigades' work is often extolled in state propaganda, and there are few signs that Kim's regime is willing to dismantle the dolgyeokdae system amid the detente.

In fact, Kim is accelerating a construction campaign in North Korea, experts say, in apparent anticipation of possible tourists and foreign investment.

Jiro Ishimaru, a Japanese journalist and North Korea expert, says this suggests the work brigades will be pressed into even more projects. Kim himself has made highly publicized visits to tourism projects such as the Wonsan-Kalma coastal resort and thanked dolgyeokdae workers for their efforts.

Rodong Sinmun, the official Workers' Party newspaper, wrote this year about the worker from Lee's August 28 brigade - named for North Korea's youth day - who begged from his hospital bed to be allowed to go back to work after an accident. The story offered no details that could verify the account. But, for the state, the propaganda message is what counts.

"What he chose over happiness was productive work through blood and sweat," the newspaper wrote. "The beauty of our once-in-a-lifetime youth lies in such exhaustive dedication for the mother nation."

The Washington Post interviewed three North Korean defectors who had worked in the dolgyeokdae, including one who worked last year building railway lines, and one who had worked as a supervisor for a decade, who said a major part of his work was to capture workers trying to escape.

All described horrendous working conditions, with workers often malnourished, sleeping at night in their work clothes in flimsy temporary housing, even in the bitter cold of North Korea's severe winter, and working with makeshift tools or their bare hands.

No safety precautions were in place, and workers often had to forage to feed themselves.

Families whose sons or daughters died in accidents were initially given black-and-white television sets as compensation, but even that practice stopped in recent years, they said.

"Sweatshop North Korea," a 2016 report by Open North Korea, a human rights group, estimated that 400,000 workers are forced into dolgyeokdae, with women also being regularly forced to supply labor through neighborhood groups and workplaces, and schoolchildren also regularly forced to do mass agricultural work.

The South Korean president appears to be focused on building engagement with the North and avoiding sensitive topics, such as human rights, that could derail his efforts. During his September visit, Moon beamed and waved at the crowds in Pyongyang that had been ordered out to welcome him.

He was driven past landmark buildings such as the Ryomyong Street skyscrapers and the Kumsusan Palace of the Sun, which defectors say were built with forced labor, afterward calling the development of the city "eye-opening" and the high-rises along the Taedong River "very impressive."

"I pay my respect to Chairman Kim's leadership to improve the people's lives amid difficult circumstances," he said in his opening statement on the first day of his three-day visit.

In October, Moon told the BBC that the human rights situation in North Korea was a problem but could not be resolved through international pressure.

"The most realistic way to improve rights of North Korean residents would be North Korea's cooperation with South Korea or the international community, and North Korea getting on a path to opening up and becoming a normal state," he said.

South Korea's Ministry of Unification declined to comment.

But Joanna Hosaniak, deputy director general of the Citizens' Alliance for North Korean Human Rights, claimed that the Moon government has shown no interest in hearing from human rights organizations that focus on North Korea.

"When they say about this building railroads and so on, how will you make sure that these are not slaves that are used on these building projects, either prisoners or women that are mobilized through the Women's League?" she asked.

Earlier this year, 200 nongovernmental groups signed a letter to the government in Seoul urging that Moon put human rights on the agenda at his first summit with Kim, she said.

"Why are we always lowering our standards and international standards to North Korean standards?" Hosaniak asked.