Chinese authorities formally arrested 18 leaders of a major underground church, clearing the way for their prosecution and potential prison sentences of up to three years. 

According to Reuters, which reported the arrests Wednesday citing a Christian NGO advocate, nearly 30 pastors and staff members belonging to Zion Church were detained by police in mid-October in the biggest crackdown on Chinese Christians in seven years.

ChinaAid, a Christian nonprofit human rights organization, said in a statement that the leaders were arrested on "politically motivated charges."

"These pastors and co-workers are being treated as criminals simply because they faithfully shepherded a large, legally unregistered church that refused to submit to CCP control and surveillance," the statement read in part.

CHINA PROVINCE FORCES PEOPLE OF FAITH TO REGISTER ON 'SMART RELIGION' APP FOR WORSHIP

Christians attend a house church service at Zion Church in Beijing, China, on April 6, 2008. (Jose M. Osorio/Chicago Tribune/Tribune News Service via Getty Images)

CHINESE UNDERGROUND CHURCH PASTOR, FATHER OF US CITIZENS, DETAINED BY AUTHORITIES, FAMILY SAYS

Dr. Bob Fu, the founder and president of the organization, called the arrests of the pastors and staff members a "chilling milestone in the CCP’s all-out war on Christianity in China."

"Their only ‘crime’ is preaching the Gospel of Jesus Christ, shepherding God’s flock, and refusing to turn Christ’s church into a propaganda tool of the Communist Party," he added. "By turning pastors into political prisoners, the CCP is not only persecuting these individuals and their families—it is sending a warning to every independent church in China: submit to Party control or face destruction."

Jin Mingri, head pastor of the Zion Church, poses in Beijing on Sept. 12, 2018, days after officials shut down one of China’s largest underground Protestant churches. (Fred Dufour/AFP via Getty Images)

CLICK HERE TO DOWNLOAD THE FOX NEWS APP

Secretary of State Marco Rubio denounced the detentions of the Zion Church members in October and asked the Chinese government to release them. 

Open Doors, an international organization that supports persecuted believers, estimates there are more than 96 million Christians in China.