North Korea's leaders should be brought before an international court for a litany of crimes against humanity, including mass murder, enslavement and starvation, a UN team said Monday.

A hard-hitting report detailed "extermination, murder, enslavement, torture, imprisonment, rape, forced abortions and other sexual violence" in the nuclear-armed totalitarian state.

"In many instances, the violations of human rights found by the commission constitute crimes against humanity," said the Commission of Inquiry on North Korea report.

"The gravity, scale and nature of these violations revealed a state that does not have any parallel in the contemporary world."

The 400-page report, which included shocking testimony from North Koreans who escaped, highlighted "the inhumane act of knowingly causing prolonged starvation".

The commission was created in March 2013 by the UN Human Rights Council. Its chair Michael Kirby said ignorance was no longer an excuse for a failure to act.

"At the end of the Second World War, so many people said 'If only we had known'," he told reporters.

"Now the international community does know," he said, adding, "the suffering and the tears of the North Korean people demand action."

Kirby said talking to people who had escaped -- including an ex-prisoner whose duties including burning starvation victims and scattering their ash as fertiliser -- made the wartime analogy brutally clear.

"I can see many parallels between the story of North Korea and the story of the Axis powers in the Second World War," he said.

North Korea refused to cooperate with the commission, claiming its evidence was "fabricated" by "hostile" forces.

Denied access to North Korea, the commission held hearings in South Korea and Japan with 320 North Korean exiles.

A frustrated Kirby wrote to North Korean leader Kim Jong-Un -- the third ruler of the communist dynasty founded by his grandfather in 1948 -- on January 20 asking him to put his side.

Kirby told Kim that any North Korean official who "commits, orders, solicits or aids and abets crimes against humanity" is responsible and must be held accountable.

Pressed by reporters, he did not accuse Kim directly, but said that "everything comes together through the supreme leader," and that the total number of perpetrators could be in the hundreds.

- China opposed -

The United States welcomed the report, saying it "clearly and unequivocally documents the brutal reality" of North Korea's abuses, while Seoul said it hoped the findings would raise international awareness.

But Pyongyang's key ally China strongly opposed any move to refer North Korea's leadership to the ICC, saying it would "not help resolve the human rights situation".

Kirby said there was "no doubt" Chinese action was needed for a breakthrough, expressing the hope Beijing would see its abusive neighbour was "a danger to itself and its region."

North Korea has long faced international sanctions over its atomic weapons programme, but activists said justice for its rights record was long overdue.

"By focusing only on the nuclear threat in North Korea, the Security Council is overlooking the crimes of North Korean leaders who have overseen a brutal system of gulags, public executions, disappearances, and mass starvation," said Kenneth Roth of Human Rights Watch.

The report condemned a system of throwing generations of the same family into prison camps under guilt-by-association rules, given testimony from former guards, inmates and neighbours.

It estimated that there are 80,000-120,000 political prisoners in North Korea, a nation of 24 million people.

Hundreds of thousands of others were believed to have perished in the camps over the past half century, "gradually eliminated through deliberate starvation, forced labour, executions, torture," the report said.

North Korean exiles in Geneva recounted the horrors they faced.

Kim Hyu Suk, born in 1962, said she was taken to a camp aged just 10 because her grandfather defected.

"During the 28 years that I lived in the camp, I lost my grandmother, my mother, my siblings, my children," she told reporters.

- Abductions 'unique' in scale -

North Koreans' daily lives were marked by constant "surveillance, coercion, fear and punishment to preclude the expression of any dissent," the report said.

It estimated 200,000 people from other countries had been abducted by North Korea or disappeared after going willingly.

Most were South Koreans stuck after the 1950-1953 Korean War ended, and ethnic Koreans who arrived from Japan after 1959.

Hundreds of South Koreans, Japanese and nationals of countries including Thailand, Malaysia, Lebanon, Romania and France have also been pressganged as language teachers or even spouses.

North Korean defectors have also been kidnapped from countries including China.

"These international enforced disappearances are unique in their intensity, scale and nature," the report said.

[Image via Agence France-Presse]