Uighur activists and their supporters on Sunday called leaked Chinese documents that revealed the government’s plans to detain millions of ethnic minorities in the Xinjiang region “truly chilling” and another form of “genocide.”

Sen. Elizabeth Warren (Mass.), a Democratic presidential candidate, tweeted her dismay after the documents were reported by the New York Times.

“The Chinese government’s cruel, bigoted treatment of Muslims and ethnic minorities is a horrifying human rights violation,” Warren wrote. “We must stand up to hatred and extremism at home — and around the world.”

The more than 400 pages of documents, leaked, according to the Times, by a member of the Chinese political establishment, included internal speeches by President Xi Jinping and other officials, information about the surveillance and control of the Uighur population and internal investigations on local officials.

The Times called the documents “one of the most significant leaks of government papers from inside China’s ruling Communist Party in decades” and a strong indication that turmoil within the ruling party is rising over the repression of the Muslim Uighurs.

The papers confirm reports that more than 1 million people have been detained in internment camps as the Chinese government seeks to strip Uighurs of their identity and indoctrinate them into being secular and loyal party supporters.

Xi still told party members in secret speeches that religious extremists should be treated with “absolutely no mercy,” the Times reported.

The documents included a script for officials to follow when explaining to students returning to the region why their parents had disappeared, the Times reported.

The World Uyghur Congress called China a “country with concentration camps” in a retweet.

“Leaks to the @NYTimes illustrate the cold, calculated nature of China’s policy of cultural genocide towards Uyghurs,” the organization retweeted.

The Washington Post reported Sunday that few Uighurs are able to escape the widespread surveillance, and even fewer are able to make it to the United States. A Uighur family now living in Northern Virginia has caught the attention of Secretary of State Mike Pompeo.

Scholars, activists and others tweeted their concerns and analysis of the leak.

Laura Murphy, a professor of human rights and contemporary slavery at Sheffield Hallam University in England, invited those who work against slavery and trafficking to collaborate.

Rose Kulak, a human rights campaigner for Amnesty International Australia, said the papers confirmed speculation about what was happening to Uighurs in the Xinjiang region.