BEIJING (AP) — The U.S. customs agency says it is holding imported goods from Chinese sports brand Li Ning after an investigation indicated they were made by North Korean labor.

U.S. law prohibits imports of goods made in North Korea or by North Korean citizens without proof they weren’t made by forced labor, according to a notice from the U.S. Customs and Border Protection in Washington.

The goods will be forfeited if Li Ning Co. cannot provide “clear and convincing evidence” within 30 days that it wasn’t made by convict, forced or indentured labor, the agency said.

It gave no details of the investigation, what goods were affected or their value.

Li Ning, founded by a former Chinese Olympic gymnast of the same name, is one of China’s most prominent athletic shoe and clothing brands.

Phone calls Wednesday to its Beijing headquarters and investor relations office in Hong Kong weren’t answered.

When asked, a Chinese Foreign Ministry spokesman, Zhao Lijian, said he was not aware of that “specific situation."

“China is firmly opposed to any form of long-arm jurisdiction and unilateral sanctions," Zhao told reporters at a briefing.

Li Ning is among a group of Chinese and foreign shoe and clothing brands that have been caught up in controversy over using materials and labor from China's northwestern region of Xinjiang. There, the ruling Communist Party is accused of detaining Muslim ethnic minorities and engaging in forced abortions and other abuses.

This month, Norway's sovereign wealth fund announced it sold Li Ning shares due to the “unacceptable risk that the company contributes to serious human rights violations” in Xinjiang.