Beijing has long claimed that IS is recruiting Uighurs from the mainly Muslim region of Xinjiang, and blamed outside forces for fomenting deadly acts of violence there and elsewhere in China that have claimed hundreds of lives.
At the same time, authorities have banned or strictly controlled the observance of certain Muslim practices, such as growing beards and fasting during Ramadan, saying they are symbols of "Islamic extremism".
Those policies "could be a push factor driving people to leave the country and look elsewhere for a sense of 'belonging'", the Washington, DC-based New America Foundation wrote in a study of leaked registration documents for IS fighters.
Of those, 114 came from Xinjiang, the study says, making it the fifth highest contributor of fighters among the provinces and regions named in the data -- after three areas in Saudi Arabia and one in Tunisia.
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Overall, recruits were more likely to come from "regions with restive histories and tense local-federal relationships", the report said.
The nominally autonomous Chinese area offered IS rich recruitment potential due to "significant economic disparities between the ethnic majority Han Chinese and the local Uighur Muslim population" and "substantial state repression", it said.
Britain's upper house passed an order last week adding the group to a list of terror organisations.
But many independent experts doubt the strength of overseas Uighur groups and their links to global terrorism, with some saying China exaggerates the threat to justify tough security measures in the resource-rich region.
All the Xinjiang recruits named in the IS documents listed their place of origin as Turkestan or East Turkestan, the name for the region often used by separatists.
On average, the fighters from Xinjiang were less educated, less well travelled, and more likely to be married than others who sought to join IS. They also claimed only a low level of religious training.
The data included a number of registration forms for children, including one as young as 10, the paper said, and "several of the forms for these children explicitly stated they joined ISIS with their families".