For 16 years, North Korea has been ranked the “most oppressive place in the world for Christians,” and this week the U.S. State Department re-asserted it as one of the world’s worst religious persecutors – torturing and executing those even suspected of worshipping God. But that still hasn’t stopped an estimated 36 percent of the population – around 9 million – from practicing Christianity.

“Life is extremely difficult for all North Koreans, but Christians face an even tougher road,” Jeff King, president of International Christian Concern told Fox News.

“Christians are accused of being imperialists seeking to overthrow the government and those who are caught practicing their faith are arrested, horrendously tortured, imprisoned and [sometimes] immediately put to death.”

So how do these brave devotees do it in the most closed country on earth?

On the surface, Christianity does exist in North Korea. Its constitution on paper vows to protect religious freedom and forbids discrimination based on one’s faith. Thus, the capital, Pyongyang, is currently host to five state-controlled churches – the Protestant Bongsu, Chilgol and Jeil Churches, the Catholic Jangchung Cathedral and the most recent being the Orthodox Holy Trinity Russian Church. Yet all are deemed to be little more than fraudulent showpieces for visiting officials and tourists.

Foreign visitors are routinely paraded around these sites, in which aptly dressed church officials clutch Bibles and bow at the altar. But Chad O’Carroll, managing director of the Seoul-based news and analysis firm Korea Risk Group, told Fox News that these are generally just hand-picked state workers whose vocation is to feign religion. The collection plates are passed through congregations and locals appear to donate as foreigners look on, but the plate ends up empty at the end.

“Guides often complain about having to go to church and put on the show because some diplomatic figure is in town,” he continued. “There’s a mosque in Pyongyang to keep the Iranian officials happy, and the Russians have their church.”

Indeed, the Russian Embassy to North Korea boasts that the decision to build the first Orthodox Church was made in 2002 after former leader Kim Jong il visited a church on an official trip to the Russian Far East. The Russians state that their Orthodox Church donated bells, icons and church utensils to the project, and that services are held every Saturday and Sunday and that the Russian Embassy “traditionally invites heads and personnel of the diplomatic missions and international organizations to participate in services on the biggest Christian holidays, such as Christmas and Easter Holiday.”

But below the surface, there is an authentic Christian movement – with extreme risk. It is estimated that there up to 70,000 Christian prisoners in concentration camps in North Korea, and the Database Center for North Korean Human Rights conjectures that more than 75 percent of Christians who are dealt this fate do not survive. Defectors have spoken of Christians being crushed by steamrollers and used to test biological weapons, or hung on a cross over a fire.

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One of the biggest obstacles Christians face is paranoia and snitching from even close confidantes, as the Kim Jong Un regime encourages tattling for rewards.

“A famous saying in North Korean culture is: 'The walls have eyes and the fields have ears.’ Christians must be extremely careful to hide their faith as much as possible, they must practice in the dark and be very wary of neighbors, friends and family members turning them in as all citizens must spy on each other,” King said. “Most parents refrain from introducing their children to the Christian faith until they are older in order to protect the family.”

Case in point: Vernon Brewer, founder and president of humanitarian organization World Help told Fox News that he often thinks about a case involving a girl named Eun, whose third-grade teacher gave the class a “special assignment” to go home and “look for a book” and if it’s the right book, the student will be honored. Eun ended up finding a Bible.

Defectors have spoken of Christians being crushed by steamrollers and used to test biological weapons, or hung on a cross over a fire.

“The next day she received a prize at her school. But when Eun returned home, her parents weren’t there,” he recalled. “It’s hard to imagine such cruelty that would unknowingly turn children on their own parents.”

Not only does the regime jail suspected culprits without trial, but they will often snatch up relatives – irrespective of whether they share the Christian belief – and are known to punish families up to three generations, Brewer said.

Parents brave enough to share their faith with their children, or extended families, are known to gather in lightless back rooms of their homes where they can only whisper their prayers and hymns. Often their Bibles are scattered pages to disguise “the book.”

North Koreans are sometimes granted permission to visit China, where some are believed to access Bibles and other Christian literature and smuggle them back in -- at their utmost peril. O’Carroll also pointed out that Christian missionaries sometimes operate orphanages and other services in border areas, but they do this without any religious symbolism.

“They preach and practice through their actions rather than traditional ways,” he explained.

From the late 19th century until the Korean War, North Korea was a Christian stronghold – and Pyongyang was considered the “Jerusalem of the East.” While it is now anything but friendly to the faithful, activists claim Christianity is still burgeoning in the deeply tyrannical country.

“Despite efforts to eradicate Christians, we have found the church is North Korea is actually growing,” Brewer added. “They know only God is powerful enough to break through the darkness of the most oppressive regime on earth.”