GENEVA (Reuters) - A leading researcher on China’s ethnic policies said on Wednesday that an estimated 1.5 million Uighurs and other Muslims could be held in so-called re-education centers in Xinjiang region, up from his earlier figure of 1 million.

FILE PHOTO: A gate of what is officially known as a vocational skills education centre under construction in Dabancheng, in Xinjiang Uighur Autonomous Region, China, September 4, 2018. REUTERS/Thomas Peter/File Photo

China has faced growing international opprobrium for what it says are vocational training centers in Xinjiang, a vast region bordering central Asia that is home to millions of ethnic minority Muslims. Beijing has said the measures are needed to stem the threat of Islamist extremism.

The governor of Xinjiang, Shohrat Zakir, said on Tuesday that China is running boarding schools not concentration camps or re-education camps in the remote region.

Adrian Zenz, an independent German researcher, said that his new estimate was based on satellite images, public spending on detention facilities and witness accounts of overcrowded facilities and missing family members.

“Although it is speculative it seems appropriate to estimate that up to 1.5 million ethnic minorities - equivalent to just under 1 in 6 adult members of a predominantly Muslim minority group in Xinjiang - are or have been interned in any of these detention, internment and re-education facilities, excluding formal prisons,” Zenz said at an event organized by the U.S. mission in Geneva, home of United Nations human rights bodies.

“The Chinese state’s present attempt to eradicate independent and free expressions of the distinct ethnic and religious identities in Xinjiang is nothing less than a systematic campaign of cultural genocide and should be treated as such,” Zenz added.

The U.S. State Department on Wednesday sharply criticized human rights violations in China, saying the sort of abuses it had inflicted on its Muslim minorities had not been seen “since the 1930s”.

Omir Bekali, a Kazakh Uighur, told a panel at the event that he had been tortured by Xinjiang police and held in a camp for six months in a small room with 40 people.

“We had to applaud the Communist Party, sing songs about (Chinese leader) Xi Jinping and say thanks for the government. We had no right to talk,” he said.

A bipartisan group of U.S. lawmakers complained to the Trump administration this week that its response to rights abuses against China’s Muslim minority was inadequate, months after it said it was looking into imposing sanctions.

At the Geneva event, U.S. ambassador Kelley Currie, of the State Department’s office of global criminal justice, was asked about imposing such sanctions on China.

“We are always looking at all of the mechanisms and the tools that we have available to us to identify those who are responsible for serious and gross human rights abuses and to ensure that they don’t benefit from opportunities to travel to the United States and that we don’t give them access to the U.S. financial system,” she told reporters, declining to be specific.