More than one million Muslims are being detained and “re-educated” in secret camps in western China, according to a UN human rights panel.

On Friday, a panel of U.N. human rights experts said Muslims in China are being treated as “enemies of the state” and announced that it had received “credible reports” about the “arbitrary and mass detention of almost 1 million Uighurs” in “counter-extremism centers” known as “re-education camps” in China.

The camps in China’s northwest Xinjiang province have drawn international attention this year, as academic researchers used satellite photos and government construction bids to establish the vast scale of the program. China legal expert Jerome Cohen has called the internments the largest-scale detentions outside the judicial system in China since Mao Zedong’s “anti-rightist” campaigns of the 1950s.

WSJ reports: The Chinese government has battled a sporadically violent, Uighur-led separatist movement in Xinjiang for decades. Chinese officials say the movement is an outgrowth of religious extremism and describe its members as terrorists.

Human-rights groups say the violence is in reaction to government-sanctioned discrimination against Uighurs and other Muslim ethnic minorities and restrictions on their ability to practice Islam.

Abdurehim Gheni, a Uighur activist living in exile in Amsterdam, said family members told him in May last year to stop contacting them because police were harassing them over his work protesting discrimination against Uighurs in Xinjiang. He said he later heard from friends in his hometown of Aksu that one of his brothers had been sent to undergo re-education, but he hasn’t been able to glean any information about his relatives since.

“I believe the Chinese government’s goal is to completely erase the Uighur ethnic identity,” said Mr. Gheni, who traveled to Geneva to take part in the U.N. meetings. “If you speak up, then your family members will be sent to a re-education camp.”

The U.S. State Department said last month that it was “deeply concerned” about the camps and the accompanying campaign against Chinese Muslims, noting that there were reports of deaths in the camps.

Beijing’s statements on Monday came at its review by the U.N. Committee on the Elimination of Racial Discrimination, which takes place every four years in Geneva. Until this week, China has said little about its Xinjiang program on a national level, though the centers have long been discussed openly by local officials.

Hu Lianhe —deputy director general of the ninth bureau of China’s United Front Work Department, which oversees Xinjiang—gave China’s fullest defense of the centers to date on Monday.

“There is no arbitrary detention” in Xinjiang, he said, adding that criminals have been imprisoned as part of antiterrorism campaigns and that those who have committed lesser offenses are sent instead to “vocational education.”

Human-rights activists criticized the remarks, saying the detention of at least hundreds of thousands of people without formal charges or trials was being recast by Beijing as a form of aid.

“In fact, they are indefinitely detaining people in unlawful facilities without charge or trial,” said Maya Wang, a researcher for Human Rights Watch.

Mr. Hu also defended some of China’s other strict policies for Muslims. He said burqas, or “masked robes,” were banned in Xinjiang to fight extremism and because they aren’t traditional garments for Uighurs, a Turkic ethnic group of Central Asia.

Mr. Hu touched upon the widespread confiscation of Uighurs’ passports in 2016—which Uighurs interviewed by The Wall Street Journal said included women, children and the elderly. Xinjiang “prevents the entry of foreign terrorists and extremists and the exit of internal terrorists and extremists,” Mr. Hu said.