The potential forced repatriation of a significant number of North Koreans, who rights groups claim face imprisonment and mistreatment at the hands of North Korean officials, prompted South Korea to announce on Friday that it has protested to China.

According to Koo Byoung-sam, a spokeswoman for the South Korean Unification Ministry, any forced repatriation of North Koreans violates international conventions and is regrettable in South Korea.

“It appears to be true that a large number of North Koreans in China’s three northeast provinces have been repatriated to the North,” Koo said.

South Korea had been unable to determine the number of people involved and whether there were defectors among them.

“The South Korean government regrets the situation and raised this matter with the Chinese side in a serious manner, emphasizing our position,” he said.

Former North Korean diplomat Tae Yong-ho, who is now a member of South Korea’s parliament, issued a statement calling on the foreign ministry to summon the Chinese ambassador to South Korea as a form of protest.

A Chinese foreign ministry spokesperson said on Thursday there were no “so-called defectors” in China, when asked about a report Beijing had deported about 600 North Korean defectors this week despite an appeal by South Korea.

On Friday, the same spokesperson said China would “continue to appropriately handle” the matter according to humanitarian principles as well as domestic and international law.

China has never recognised fleeing North Koreans as defectors and instead calls them “economic migrants”.

South Korea’s government and international rights organisations have said defectors who are deported back to the North face harsh punishment including detention at labour camps where they are subject to dangerous treatment and conditions.

Human Rights Watch said Chinese authorities had forced back more than 500 North Koreans, most of them women, and it called on governments to denounce the expulsion by Beijing.

The North Koreans were taken in vehicle convoys on Monday night over five separate border crossings into the North, the rights group said, citing a missionary with contacts in the North and China who worked to help defectors.

A North Korean who defected to South Korea in 2001 said a cousin of his, who had lived in China for 25 years, and had a daughter with a Chinese man, was believed to be among those deported this week.

The defector, Kim Hyuk, told Reuters his cousin, Kim Cheol-ok, was detained by Chinese authorities in Jilin province in April and had in recent days called her daughter from prison to say she was about to be sent to back to North Korea.