Chinese authorities detained at least 80 Christians in a raid on a prominent church that operates outside the umbrella of the Beijing government's official Protestant organization, an advocacy group said Monday.

Texas-based ChinaAid said the pastor of the Early Rain Covenant Church and his wife were among those detained in the southwestern city of Chengdu starting Sunday night.

China has cracked down heavily on independent church groups this year as part of a move to suppress all religions. The government requires that Protestants worship only in churches recognized and regulated by the Three-Self Patriotic Movement. Even within that framework, the officially atheist ruling Communist Party has been seeking to rein in religious expression, including removing crosses from official and unofficial churches.

Early Rain is believed to have several hundred members who meet in different locations around Chengdu, a sprawling city with a population of nearly 15 million.

Many of those detained, including church pastor Wang Yi, were seized from their homes overnight Sunday, ChinaAid said.

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"The massive overnight attack against members of the independent, renowned Early Rain Covenant Church represents a major escalation of religious persecution in China," Bob Fu, ChinaAid's founder and president, said in a statement on the group's website.

The crackdown, which extended into international Human Rights Day on Monday, shows the administration of President Xi Jinping is "deliberately making itself the enemy of universal values, such as religious freedom for all," said Fu, who is a close friend of Pastor Wang.

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Tens of millions of Chinese identify as Christians, most of them Protestant, and their ranks have been increasing rapidly despite the Communist Party's efforts to limit them. Their numbers rival the membership of the ruling party, which stands at around 90 million.