Prison guards in Communist North Korea struck the heads of Christian detainees suspected of Bible study until "blood spurted upwards", according to a new report from human rights organisation Korea Future.

Between November 2019 and August 2021, Korea Future investigators interviewed survivors, witnesses, and perpetrators of religious freedom violations who had escaped from the Communist dictatorship to democratic South Korea.

The resulting report examines 167 human rights abuses against 91 Christians in prison camps between 1997 and 2018.

The North Korean criminal code classes Christianity as a "political crime", with Christians being sent to harsh and secretive "political" prisons.

In some cases they are given "indefinite life sentences", the study found.

The report, released on Wednesday, documented evidence that victims were subject to physical beatings "with objects, fists, and feet; to the ingestion of polluted food; to positional torture; to sleep deprivation; and to forced squat jumps".

A Christian who was detained at the Onsong County Ministry of State Security Detention Centre observed how "correctional officers would make detainees suspected of studying the Bible stick their heads between the steel bars of a cell door".

The guards would then strike the detainees' heads until "blood spurted upwards".

In another case, a young woman had been arrested while in possession of a Bible, prompting officials from the Ministry of State Security Central Command to beat her with a wooden stick until a superior intervened after hearing the victim screaming.

"In some cases, the physical beatings of victims were so severe that it contributed to their premature deaths", the investigators found.

One victim who was a member of an underground church was beaten so severely in 2019 while in detention that they later died from their injuries.

"Few underground churches are known to exist in North Korea," the report says, "yet even their presumed existence prompts Ministry of State Security-run investigations to last years and involve multiple branches."

In one recent case, an individual had formed an underground church with a family to meet for communal prayer. Most of its members had been introduced to Christianity in China and "their church was supported by donations from persons outside of North Korea who also provided notebooks so that the church's small congregation could copy passages from the Bible.

"The exact size of the congregation is unclear, but by 2019 there were 16 members. Most were women," the report reveals.