Prisoners who have attempted escape from North Korean jails have been publicly executed while other inmates are subject to sexual violence and beaten with clubs, according to a UN report.

Guards make detainees undress and repeatedly subject them to body searches for money and concealed items, while their cells are so overcrowded they cannot lie down, the report to the UN General Assembly said.

The secretary-general Antonio Guterres said the UN human rights office received and analysed accounts of North Koreans who had experienced detention, the vast majority of them women who escaped initially to China.

Between September and May, the office interviewed more than 330 individuals who left the country, Mr Guterres said.

The former detainees alleged “gross violations of the rights to life, liberty and security of the person” perpetrated by security officers.

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North Korea has repeatedly said it does not violate human rights.

According to Mr Guterres, “former detainees report extremely unsanitary conditions, and insufficient food causing malnourishment, illness, and occasionally also death of other detainees”.

Reports received by the human rights office “include cases of sexual violence by prison officials against female detainees, including during invasive body searches,” the UN chief said.

During pre-trial periods, detainees are provided no access to lawyers, and “accounts reveal that detainees are simply informed of their prison sentences at the end of the investigation, particularly in cases where the accused is sentenced to up to six months in a short-term labour camp,” he said.

The secretary-general said arrests, beatings, forced labour, executions and other abuses perpetrated in detention centres and prisons by officers from the Ministry of State Security and Ministry of People’s Security “appear to be carried out in a widespread and systematic manner”.

He said people in political prisons, ordinary prisons, and detention facilities were all subject to forced labour “in dangerous conditions, without adequate food, access to medical care and living conditions that meet international standards”.

Mr Guterres said accounts documented by the UN human rights office also revealed “the prevalence of corruption” in North Korea’s penal system.

“Bribes can be paid to avoid arrest and detention, to mitigate or avoid prison sentences, to avoid beatings, to ameliorate the harshness of the forced labour required, and to secure family visits,” he said.