The report by the Transitional Justice Working Group (TJWG) came about two months after South Korea lodged a protest with China over the suspected repatriation of a large of number of North Koreans who were trying to flee to South Korea.

The TJWG said hundreds of defectors were transported in guarded buses and vans from Chinese detention centres across the border into the North on Oct. 9, calling the incident the largest such mass repatriation in years.

The identity of the defectors remains unknown, but most of them are women, it said.

“No communication has been established with the defectors since they were sent back,” the group said in a statement. “Those forcibly returned face the prospect of torture, sexual and gender-based violence, imprisonment in concentration camps, forced abortions and execution as their authoritative regime brands them ‘criminals’ and ‘traitors.'”

North Korean state media has not commented on the case, but had long denounced defectors as “human scum”, and leader Kim Jong Un has tightened borders further over the past few years.

Beijing’s foreign ministry denied in October that there were “so-called defectors” in China, but said that North Koreans had illegally entered for economic reasons, and that China always handled the issue according to the law.

Seoul’s unification ministry and foreign ministry did not immediately comment on Thursday.

North Korean defectors arriving in the South had hit an all-time low during the pandemic when North Korea sealed its borders.

Pyongyang has since lifted some coronavirus restrictions and resumed trade and other exchanges with China. Beijing’s customs data has indicated a sharp increase in exports to North Korea in recent months.

(Reporting by Hyonhee Shin; Editing by Ed Davies and Gerry Doyle)