North Korea views religion as a threat to its state ideology
Human rights groups in South Korea say North Korea has stepped up executions of Christians, some of them in public.
The communist country, the world's most closed society, views religion as a major threat.
Only the founder of the country, Kim Il-sung, and his son, Kim Jong-il, may be worshipped, in mass public displays of fervour.
Despite the persecutions, it is thought up to 30,000 North Koreans may practise Christianity secretly in their homes.
A report by a number of South Korean groups highlights one particular case of a woman allegedly executed in public last month, in a northern town close to the Chinese border.
She was accused of distributing Bibles, spying for South Korea and the United States and helping to organise dissidents.
Her parents, husband, and children were sent to a prison camp.
Such reports are hard to verify, but North Korea is known to be intolerant of religion - it views any form of alternative social organisation as a competitor for its own, religion-like ideology.
The US government says just owning a Bible in North Korea may be a cause for torture and disappearance.
Pyongyang's position appears to have hardened on everything from human rights to defence policy and international relations in the last year or so.
It is thought this may be a way to shore up the government through Mr Kim's illness and the process of anointing his youngest son, Kim Jong-un, as North Korea's next leader.