A North Korean prison on the border with China has expanded detention facilities for female inmates in an indication that a growing number of women are forcibly repatriated from the neighboring nation, a U.S.-based human rights group said Tuesday.

Satellite imagery confirms the expansion of the Jongori reeducation camp, also known as reeducation camp No. 12, in the North's northern city of Hoeryong, bordering China, the Committee for Human Rights in North Korea said in a joint report with AllSource Analysis.

According to the report, the prison's population is estimated to have increased from 1,300 in the late 1990s to about 5,000 in recent years. It also said that 25 percent of the prisoners are reportedly women and some 80 percent of the female prisoners are North Korean nationals forcibly repatriated from China.

"Their detention highlights the illegality of China's forcible repatriation of North Korean refugees to conditions of danger, despite overwhelming and justified fear of persecution, in direct violation of the 1951 UN Convention relating to the Status of Refugees, to which China is a party," HRNK Executive Director Greg Scarlatoiu said.

China does not recognize North Korean defectors as refugees and regularly repatriates them to their home country, where they can face harsh punishment. But Beijing has allowed North Korean defectors involved in high-profile cases or those who sought refuge at foreign diplomatic missions to travel to South Korea to avoid international opprobrium.

Tens of thousands of North Koreans are believed to be in hiding in China, hoping to travel to Thailand or another Southeast Asian country before resettling in South Korea, which is now home to about 27,000 North Korean defectors. (Yonhap)