GENEVA — A United Nations human rights investigator voiced concern on Thursday over the unknown fate of nine young North Korean defectors, some of them children, who were sent back to China from Laos after trying to cross the border this week.

Chinese authorities are obliged under international law not to return them to North Korea, where they could face persecution and even death, said Marzuki Darusman, U.N. special rapporteur on the Democratic People's Republic of Korea (DPRK).

"I have very real concerns about the penalties and treatment they could face if returned to DPRK and all the concerned authorities have an urgent responsibility to ensure their protection," Darusman said in a statement issued in Geneva.

"No one should be refouled [forced back] to DPRK, where they may face persecution or severe punishment, including torture and the death penalty," he said.

North Korea's only land border is with China, and many people fleeing the north travel through China in the hope of reaching other countries.

The nine youths, all believed to be orphans, were sent back to China on May 27 after being arrested by Laotian police, Darusman said.

"I am extremely disappointed that the Laos Government appears to have abdicated its protection responsibilities in this way, and I urge the Chinese authorities not to do the same," he said.

North Korean authorities consider it a criminal offense to leave the country without official permission, according to Darusman's latest report.

Darusman, a former attorney-general of Indonesia serving in the independent post, is part of a commission of inquiry launched in March to investigate violations and possible crimes against humanity in North Korea.

The three-member commission is expected to focus on allegations of torture and labor camps in North Korea believed to hold at least 200,000 people, activists say. Pyongyang denies the existence of such camps and is not expected to cooperate.

The U.N. General Assembly has expressed serious concern about the situation of refugees returned to North Korea and the punishments they can face.