GENEVA — China issued a blanket denial on Monday of accusations from United Nations experts that it had detained more than a million ethnic Uighur Muslims in re-education camps in the western region of Xinjiang.

Beijing has progressively tightened security in Xinjiang since an eruption of violence there in 2009, but the crackdown has escalated since 2016, when a new Communist Party secretary for the region began widely expanding security services and surveillance.

Gay McDougall, a member of the United Nations Committee on the Elimination of Racial Discrimination, spoke of the region on Friday as becoming “something resembling a massive internment camp,” with mass detention, re-education and disappearances.

At a hearing in Geneva on Monday, a 49-strong Chinese delegation met questions from the committee with flat contradiction.