A Christian lawyer who had been advising churches in China's Zhejiang province that are resisting government orders to remove crosses from church roofs faces up to six months in secretive detention after the police detained him and accused him of threatening state security.

As reported by the Gospel Herald, Zhang Kai, who is from Beijing, was taken into custody last week while advising a church in Wenzhou, a commercial city commonly referred to as "China's Jerusalem" due to its large Christian population.

Over the past year, Mr. Zhang was helping members of the city's Christian community who have actively fought the Communist government's efforts to remove crosses from church rooftops and reduce the presence of churches in the area.

"Christianity teaches us to submit," Mr. Zhang said in July of his decision to help churches fight the government order, according to Initium Media. "But what we ought to submit to is the Constitution and morality, not to illegal people and conduct."

According to Yang Xingquan, a colleague of Mr. Zhang's, the Christian lawyer was detained by state police and charged with endangering state security and "assembling a crowd to disrupt social order," a charge that could place him under secretive detention for six months.

"We haven't been told where Zhang Kai is or really why he's been detained," Mr. Yang said told reporters, revealing he had spoken to a police officer involved in the case, who told him Mr. Zhang was being held under a form of detention called "residential confinement."

"We're still waiting to see whether we'll be allowed to see him," Mr. Yang said, citing comments from a police officer involved in the case. "Next, we'll try to understand the circumstances and speak to people who had contact with him."

The New York Times notes that in the past, the police have used residential confinement to "detain dissidents in secret without trial or access to lawyers or family," citing security concerns.

While China claims to guarantee freedom of religion, the government has exhibited a growing discomfort with Christianity, whose followers are said to rival in number the 86 million members of the Communist Party.  

Thus far, more than 1,200 crosses have been removed and several churches have been completely demolished by government forces. Amnesty International estimated last month that more than 230 protesters have been detained over the last year, and at least 23 people, many of them pastors, still remain in police custody.

On Tuesday, the U.S. ambassador for religious freedom, David Saperstein, called for Mr. Zhang's release, saying such detentions are a "particularly alarming development" that underscores "the precariousness of religious life in China."

"There can be no excuse for the detention of these religious figures that either met with me or tried to meet with me," said Saperstein, who met with Chinese government officials on religious freedom, the AP reports. "These detentions fit into a disturbing pattern of state intimidation of public interest lawyers, Internet activists, journalists, [and] religious leaders," he added.