South Korean President Park Geun-Hye warned North Korea on Monday that it would be held responsible for the safety of nine young asylum seekers forcibly repatriated after their capture in Laos.
"What's most important is to ensure (their) lives and safety, and that they will not receive unfair punishment," Park told a meeting of senior aides.
"Otherwise, North Korea cannot avoid international criticism and responsibility for their human rights," she said.
The case of the nine escapees has garnered international attention, partly because of their youth and reports suggesting they are all orphans.
Confirming their arrest on May 10 for illegal entry, the Lao foreign ministry said Monday that all nine were aged 14 to 18.
Two South Korean nationals were detained at the same time for alleged human trafficking and handed over to the South Korean embassy, a ministry statement said.
The nine were taken to China on May 27 and then flown back to Pyongyang the following day.
Most North Korean refugees begin their escape by crossing into China and then try to make it to a third country -- Thailand is the most popular choice -- where they generally seek permission to resettle in South Korea.
The foreign ministry in Seoul has come under fire after it emerged that its embassy in Vientiane had been aware of the refugees' arrest but had been unable to prevent their return to China.
Describing the repatriation as a "very regrettable incident that should have never happened", Park said her government would seek to ensure that "major defection routes" used by North Korean refugees remain open.
Laos is seen as a relatively safe transit point, but moving refugees through the country is still an illicit operation that requires guards and officials to be bribed.
"If at any point the smuggling network fails and they are taken into official custody, it's a different story," said Phil Robertson, deputy Asia director at Human Rights Watch.
"In this case they were taken to Vientiane, and once that happened there wasn't much likelihood that the Lao authorities would tell the North Koreans they were handing them to South Korea," Robertson said.
"It's up to the international community to pressure Laos to uphold the principle of not returning refugees," he added.
In Geneva, Rupert Colville, spokesman for the UN high commissioner for human rights, slammed Laos and China for ignoring their "obligations" under international law.
"We are extremely concerned for the protection of this group, which includes up to five minors, who are at risk of severe punishment and ill treatment," Colville said.
"The situation of returnees to North Korea has been a constant source of concern for many years. They can receive very severe punishment merely because they have left the country," he said.
In Washington, State Department spokeswoman Jen Psaki said the United States was "very concerned" and urged China and Laos to cooperate in the protection of North Korean refugees within their territories.
She also urged North Korea to allow independent monitors immediate access to the group.
Beijing reacted angrily to what it described as Colville's "irresponsible remarks" and appeared to try and distance itself from the North Koreans' return.
"In the whole process, China has not received a request by any party to assist in the repatriation of these persons," foreign ministry spokesman Hong Lei told a regular briefing.
North Korean leader Kim Jong-Un is believed to have tightened border controls since he came to power after the death of his father Kim Jong-Il in December 2011.
Since the end of the Korean War in 1953, some 25,000 North Koreans have escaped -- most after a deadly famine in the mid-90s -- and settled in the South.
The number of refugees arriving in South Korea plunged more than 40 percent to 1,508 last year.
