BEIJING — The German soccer star Mesut Özil is the latest international sports celebrity to be at the center of controversy over China’s hard-line policies, igniting fury among Chinese internet users by denouncing the country’s mass detention of Muslims.

Mr. Özil, who is of Turkish heritage and plays for Arsenal, an English Premier League club, took on one of China’s most sensitive policies with his comments on Friday about Uighurs, a largely Muslim Turkic minority in Xinjiang, in northwestern China.

The Chinese authorities have held as many as a million Uighurs, and possibly more, in indoctrination camps meant to drastically weaken their commitment to Islam. The internments have drawn international anger and led to legislation in the United States Congress that could impose sanctions on Chinese officials over the detentions, which China says are intended to deter terrorism.

“They shut down their mosques. They ban their schools. They kill their holy men. The men are forced into camps and their families are forced to live with Chinese men,” read identical posts on Mr. Özil’s Twitter and Instagram accounts, according to a translation by The Guardian.