CANBERRA, Australia—Chinese authorities aggressively expanded the scale of internment camps in Xinjiang this year, according to a new study, even as China’s program of mass detentions of Muslims in the region started to draw international scrutiny.

An examination of satellite imagery released Thursday by intelligence analysts from an Australian security think tank mapped the expansion of 28 detention camps in the restive frontier region. Their analysis found that total floor area of these facilities grew more than 465% from...