Former North Korean defectors participate in a rally to demand release of North Korean refugees captured in China near the Chinese Embassy in Seoul on March 2. The protesters called for China not to send North Korean refugees back to their country, saying those refugees might be executed. The letters read "Oppose repatriation to North Korea." (Ahn Young-joon/AP)

Last month Chinese security officials, in the span of several days, staged a series of roundups along the country’s border with North Korea. They arrested between 25 and 33 North Korean defectors, aid workers say, and placed them in holding cells, a last stop before they would be shipped back to the North.

In limbo, awaiting possible labor camp sentences or death if repatriated, those several dozen became the focal point of an unusually noisy campaign in South Korea designed to pressure China to abandon its policy of sending defectors back to the authoritarian nation from which they fled.

Several thousand North Koreans every year risk their lives by taking a circuitous 2,500-mile journey that begins in northeastern China — just across the border from the North — and ends in a Southeast Asian country, usually Thailand or Cambodia, where defectors seek asylum and resettlement in South Korea. Along this “underground railroad” across rural China, defectors sleep in shelters or abandoned buildings, helped by religious activists and brokers. They hop from trains to buses, hoping to avoid routine checkpoints where officials ask for identification. Their main goals while in China: Don’t draw attention. Don’t get caught by Chinese authorities.

With protesters showing up almost daily at the Chinese Embassy in Seoul to decry the arrests, the underground railroad itself has recently come under the spotlight.

That attention, most non-governmental organizations say, is the surest way to pressure China on a damaging policy. China, they say, is ignoring its international treaty commitments by sending back those who face torture. So to spread the word, protesters and celebrities gather outside the Chinese Embassy here holding signs that say “Save My Friend.” A conservative parliamentarian even went on a hunger strike.

But for those who help defectors along the underground railroad, a necessary protest also feels like a dangerous one that might backfire in the short-term. They fear that China, under increasing international pressure, will treat defectors not with greater leniency but with a strict crackdown. China’s foreign ministry says it “opposes” the attempt to “internationalize and politicize” the refu­gee issue.

Those who operate underground railroads say they see no immediate evidence that China has launched a crackdown in the wake of the protests. But they anticipate one and have ordered defectors currently in China to stay put and remain indoors, perhaps for the next two or three months. The railroad is frozen, they say.

“Activists are being very cautious,” said Son Jung-hun, a Seoul-based activist who says he helps between 50 to 60 defectors annually move through China. “This could trigger the Chinese government to have a firmer stance on their policy.”

In normal times, activists say, Chinese officials, particularly at the local level, often yield to compromise after arresting defectors, and money matters far more than policy. Such officials can be flexible so long as the cases don’t land on the radar of the North Koreans or their own bosses.

For a payment of $6,000 per defector, said Simon Suh, a Seoul-based pastor who organizes one underground railroad, Chinese officials will generally release defectors and allow them to continue on their journey — provided the case never becomes public.

“Basically, we are paying them off,” Suh said.

Before the latest case became public on Feb. 14, Son, whose family is from China and who maintains a network of police and security contacts there, had already spent days trying to negotiate the release of several of the detained defectors.

“I was talking to working-level officers,” Son said. “But once it became public, they said there was no way to exercise any influence. North Korea knew about the case, and [the defectors] all had to be sent back.”

‘Inhumane and barbaric’

A tower of evidence — reports from aid groups; testimony from defectors — reflects the grim dangers facing defectors who are caught in China and forcibly repatriated.

Human rights workers and defectors describe common punishments of torture and forced labor. Prison guards force women impregnated in China to watch the infanticide of their newborns, according to a U.S. government human rights report.

In labor camps, according to testimony in Washington from North Koreans who’d been repatriated, labor begins at 5 a.m. and ends at 9 p.m. Prisoners eat fist-size corn balls and participate in late-night self-criticism sessions, chanting loyalty to the Kim family dynasty.

Technically, China classifies those who flee the North as “economic migrants,” not refugees, and the distinction is a significant one. Refugees are entitled to international protection. But migrants are not, and Beijing has a decades-old agreement to return such defectors to Pyongyang. The policy, analysts say, is largely a matter of security: A mass exodus from the North could potentially destabilize one of China’s most important allies.

North Koreans leave their country for all sorts of reasons. Some cross for business with every intention to return. Some seek food. Some seek medicine or hard currency. Many, though, want a life in the South, where they are welcomed as citizens.

But the odds of reaching South Korea are anywhere from 30 percent to 70 percent, according to defectors and aid workers. The path through China requires daring and luck. Many defectors encounter extortionists who lure them into menial jobs that last for months, if not years. Between 80 percent and 90 percent of women, according to a 2007 report, are sexually trafficked or sold as wives in a country with a surplus of single men. One North Korean defector, Lee Kyeong Hwa, who has since settled in Seoul, crossed the border 10 years ago — at age 15 — and was sold off for $500 to a farmer, she said.

Informants frequently tip off authorities who then stage raids on shelters or at bus terminals. North Korea, railroad operators say, has stationed agents of its own throughout China, some of whom pose as defectors.

“What China has done is create a violent situation in their own country,” said Suzanne Scholte, chairman of the North Korea Freedom Coalition, which works to promote North Korean human rights. “They know what they’re doing is inhumane and barbaric. And the Western world — we should be calling China on this.”

Fear of retribution

Those defectors who make it to South Korea often feel conflicted about publicizing their experiences — especially because doing so could mean retribution for family members who are still in the North or passing through China.

That’s why Hong Won-il, 53, spent seven days contemplating whether to speak outside the Chinese Embassy. He’d twice been repatriated, and he had stories about his 14 months at a North Korean labor camp, where he shriveled from 137 to 99 pounds. At that camp, Hong said, bodies were buried along a hillside in holes just 12 inches deep. “Sometimes you could see a nose sticking out of the ground,” he said.

While Hong debated, he didn’t ask friends or fellow defectors for advice. But he watched the protests on the nightly news and thought about what he should say. He also thought about his wife, his son, his daughter and his mother — all of them still living in the North.

So Hong bought a blue medical mask from a convenience store and headed one day to the embassy. He spoke for five minutes, and television cameras recorded his speech. He showed a printed-out satellite image of the camp where he once lived, and he told fellow protesters about the “flower garden” where the bodies were buried.

“I am a witness to this,” he said.

At one point during the speech, Hong tugged on his mask, exposing his face.

“I felt the very slightest hope to say something,” he later said in an interview, “because so many people are paying attention. I also felt a moral duty.”

Special correspondent Yoonjung Seo contributed to this report.