A pastor from Chongyi Church -- China's largest megachurch -- was released after spending three months in "black jail," which falls outside the country's penal system. But, he still remains under the "residential surveillance."

Pastor Gu Yuese was arrested on charges of "embezzlement," but human rights and Christian activists said that he was likely caught in the government's radar after vocally opposing state-sponsored cross-removal campaign.

The pastor was detained in January, but formally arrested on February 1 on embezzlement charges. However, the government never provided any details about the accusation.

Chongyi is a state-approved church with over 10,000 members, and Pastor Gu was held in good repute by the Communist Party before he openly protested against the cross-removal campaign since 2014, which has destroyed about 2,000 crosses. He was expelled from his position as the church leader 10 days before he was detained.

Prior to his imminent arrest, he issued an open letter addressed to his congregation, warning about a, "rare freezing, cold [set to] befall Hangzhou," which is the capital city of province Zhejiang, also called Jerusalem of China for its high concentration of Christians. He was apparently referring to the government's crackdown on crosses across the city.

"Chongyi Church is also experiencing unprecedented trials," the letter reads. "Everyone must equally rely on the Lord's grace to confront [this hardship] and triumph over it... Increasingly, we feel God's good intentions in this storm. It will refine every impurity in our ministry team to the greatest extent and compel us to love the Lord and people more purely."

It was first time since Communist dictator Mao Zedong's rule and the Cultural Revolution, that a clergy holding such a high position was arrested.

According to a Reuters report, China is conducting the worst domestic crackdown in two decades on human rights and Christians under President Xi Jinping. Nearly 1,000 rights activists were detained last year alone - and almost as many as in the previous two years combined.

Chief Executive of Christian Solidarity Worldwide Mervyn Thomas said: "We welcome news of Pastor Gu's release but note with concern that he is not actually free as he is under residential surveillance."