The detentions are emblematic of increasingly harsh restrictions targeting spiritual and educational life for Muslims in China.

Once focused on giving minorities limited cultural autonomy, China's ethnic policy has shifted in the last decade toward an approach that favors complete assimilation with China's Han ethnic majority in language and religious practice.

Chinese Muslims are most densely clustered in the northwestern regions of Gansu, Ningxia and Xinjiang, but live across the country, as they have for more than a millennium.

Chinese Muslims are most densely clustered in the northwestern regions of Gansu, Ningxia and Xinjiang, but live across the country, as they have for more than a millennium.

Most are Uighur — a Turkic ethnic group — or labeled as Hui, ethnically and linguistically indistinguishable from China's Han ethnic majority.

Chinese Muslims are most densely clustered in the northwestern regions of Gansu, Ningxia and Xinjiang, but live across the country, as they have for more than a millennium.

"What dominates Muslim [government] cadres is the [Communist] party line and the official version of Islam promoted by government agencies and organizations," says Ma Haiyun, an assistant professor at Frostburg State University, where he studies Islam in China.

Two people close to him say he remains in detention in China's northwestern Xinjiang region.

Their arrests are evidence of a crackdown widening from its epicenter in Xinjiang, where authorities have detained hundreds of thousands of Uighurs and other ethnic minorities, sentencing some to lengthy prison terms for practicing Islam.

Despite international criticism, Chinese leader Xi Jinping declared the detention and security policies in Xinjiang "entirely correct" and a "success" at a September meeting of party officials.

Uighur men walk towards the Id Kah mosque to attend prayers marking the end of Ramadan, in Kashgar in China's northwest Xinjiang region, in 2019.

Uighur men walk towards the Id Kah mosque to attend prayers marking the end of Ramadan, in Kashgar in China's northwest Xinjiang region, in 2019.

"Many people have been oppressed for their speech in China but among the Muslim community, those who get into trouble for their writing or publishing have gone unnoticed," a prominent Chinese Muslim writer tells NPR.

"They interrogated them about their relationship with several Muslim intellectuals and overseas Chinese Muslims.

As for China's Muslim community leaders, "There are no imams who dare to speak out," says a scholar who leads a Quran reading group in northwestern China.

Beginning in 2017, Chinese Muslims outside Xinjiang watched with dread as hundreds of thousands of Uighurs, a Turkic ethnic minority, were detained and sent either to "reeducation centers" or prison

Soon after, Xinjiang security officers began fanning out to other provinces to send Hui Muslims with identity documents registered in Xinjiang back to the region

One of those forcibly returned to Xinjiang was a young Hui woman who taught at a religious school in a mosque outside Xinjiang, after completing a theological studies degree at Egypt's prestigious Al-Azhar University

Others moved abroad, but even outside China, Xinjiang security officials continue to harass them through WeChat

"My hometown police somehow knew that I had even moved apartments this year," says one Hui Muslim now living in Egypt who requested anonymity for fear of retribution from Chinese security officials

Last February, during Lunar New Year holidays, two Xinjiang public security officers set up a table at one of the six mosques in the city of Sanya to register identification documents of everyone who attended Friday prayers, according to two people who attended prayers that day

Local Communist Party regulations now ban party members from practicing Islam and call for increased governance of Muslim neighborhoods in Sanya, according to the South China Morning Post

Chinese security forces have also been seeding the ranks of local branches of the Islamic Association of China, a state-run body which organizes the only officially permitted hajj pilgrimages to Saudi Arabia