The abating Covid-19 pandemic could result in up to 2,000 North Koreans being sent back to their country from China to face imprisonment or worse, US lawmakers heard in testimony on Tuesday. The experts who spoke urged the international community to pressure China and the United Nations to prevent their return.

Witnesses told the Congressional-Executive Commission on China that the pandemic – along with China’s increasingly sophisticated security systems – has darkened the outlook for North Koreans fleeing their country to work, escape persecution or unite with family.

“We have good reason to believe that such repatriation is imminent, as North Korea reopens its border following extended closure in the wake of the Covid-19 pandemic,” said Representative Chris Smith, a Republican from New Jersey. “I share this with deep concern.”

Even as Pyongyang has refused to accept foreign vaccines, it has responded to the pandemic by shutting itself off from the world. That has resulted in a backlog of North Koreans arrested by China near their shared border. They are languishing as Pyongyang refuses to take them back, witnesses said, fearful they will import the disease.

China, which considers fleeing North Koreans to be economic migrants rather than refugees, would like to send them back but has met with a refusal from Pyongyang, witnesses said. Most are kept in six known Chinese detention camps near the border, which satellite images suggest have been expanded, said Hanna Song, a director with the Seoul-based Database Center for North Korean Human Rights.

The commission, created in 2000 to advise Congress on human rights and rule of law issues in China, is comprised of nine senators, nine members of the House of Representatives and five senior administration officials appointed by the president.

North Korea’s lockdown and the growing difficulty of escaping through China have also affected the number of refugees able to make it to South Korea, experts said.