China is running hundreds of detention centers in northwest Xinjiang across a network that is much bigger than previously thought, according to research presented Thursday by an Australian think tank.

The Australian Strategic Policy Institute (ASPI) said it had identified more than 380 "suspected detention facilities" in the region, where China is believed to have held more than 1 million Uighurs and other mostly Muslim Turkic-speaking residents.

The number of facilities is around 40% greater than previous estimates, the research said, and has been growing despite China's claims that many Uighurs have been released.

Using satellite imagery, eyewitness accounts, media reports and official construction tender documents, the institute said "at least 61 detention sites have seen new construction and expansion work between July 2019 and July 2020."

Fourteen more facilities were under construction in 2020 and around 70 have had fencing or perimeter walls removed, indicating their use has changed or they have been closed.

Beijing on Thursday again denied the existence of detention sites. The government says they are vocational training centers used to counter extremism.

Foreign Ministry spokesman Wang Wenbin called ASPI "the vanguard of anti-China forces whose academic credibility is seriously questionable."

U.S. lawmakers recently voted to ban imports from Xinjiang, citing the alleged use of systematic forced labor.

Beijing recently published a white paper defending its policies in Xinjiang, where it says training programs, work schemes and better education mean life has improved.

It claims to have given "training sessions" to an average of 1.29 million workers each year between 2014 and 2019.

Following the publication of the ASPI report, the Chinese government-controlled nationalist tabloid Global Times cited "sources" as saying contributors Clive Hamilton and Alex Joske were banned from entering China.

Wang did not confirm if the two academics had been banned on Thursday, but said the matter was "totally within the scope of China's sovereignty."