Christians in North Korea face rape, torture, enslavement, and being killed for their faith, a damning new report from Christian Solidarity Worldwide (CSW) has warned.

CSW, a UK-based religious freedom charity, said in the report, Total Denial: Violations of Freedom of Religion or Belief in North Korea, that freedom of religion or belief "is largely non-existent" under dictator Kim Jong-Un's leadership.

"Religious beliefs are seen as a threat to the loyalty demanded by the Supreme Leader, so anyone holding these beliefs is severely persecuted," the report says.

"Christians suffer significantly because of the anti-revolutionary and imperialist labels attached to them by the country's leadership."

Among the documented incidents against Christians are "being hung on a cross over a fire, crushed under a steamroller, herded off bridges and trampled underfoot".

Other crimes include "extra-judicial killing, extermination, enslavement/forced labour, forcible transfer of population, arbitrary imprisonment, torture, persecution, enforced disappearance, rape and sexual violence, and other inhumane acts".

Though the regime officially says there are just 13,000 Christians in North Korea, the true figure is believed to be much higher. Cornerstone Ministries International, which works with North Korean Christians in the country as well as in China, estimates that there are between 200-300,000 in total.

Believers are forced to practise their faith in secret, and if caught, get sent to North Korea's notorious hard labour camps. One escapee told CSW that while he was detained, he met a prisoner who was sent to the camp simply because he had spent a month in China studying the Bible.

"A policy of guilt by association applies, meaning that the relatives of Christians are also detained regardless of whether they share the Christian belief," the report says.

"Even North Koreans who have escaped to China, and who are or become Christians, are often repatriated and subsequently imprisoned in a political prison camp."

Despite intense persecution, there are 121 religious facilities in North Korea, the Database Center for North Korean Human Rights says, including 64 Buddhist temples, 52 Cheondoist temples, three Protestant churches, a Catholic cathedral and a Russian Orthodox church.

All five churches are in the capital, Pyongyang, however, and analysts suggest that they may function primarily to improve North Korea's image with the international community, rather than as free houses of worship.

There are also unconfirmed reports of 500 house churches in North Korea, where individuals whose families were Christians before 1950 – when the Korean War began – are allowed to gather for worship. However, they may not elect leaders or use religious materials.

Christians are not the only religious group to suffer under the regime. Buddhists and Cheonists are also treated as revolutionaries, though the higher number of temples than churches "suggests that the regime may have a higher degree of tolerance for beliefs considered to be indigenous to Asia or to the Korean peninsula," CSW says.

However, research suggests that temples are maintained as cultural heritage sites rather than as functioning religious buildings.

"I have seen a Buddhist book once at a temple," one interviewee told the US Commission on International Religious Freedom. "It had a strap with Chinese letters and months written on it. There are temples but people are not allowed to believe in them."

"These religious facilities, organisations and institutions are designed to indicate the existence of religious pluralism and acceptance, but the reality is full of contradictions," CSW says.

The United Nations Commission of Inquiry and other sources have testified to the "use of these formal facilities, organisations and institutions for political means."

CSW has urged the international community to support the referral of North Korea to the International Criminal Court for its violations of human rights.

"The regime is actively hostile to religion and religious believers, both domestically and internationally. Many North Koreans are suffering because of their faith, and the international community needs to act urgently to end impunity and ensure accountability," it said.

"The UN and other members of the international community must ensure that human rights are central in any negotiations with North Korea... Every effort must be made to seek accountability and justice for the North Korean people, who suffer human rights abuses on a scale unparalleled in the modern world."