The international community must act on evidence that crimes against humanity are being committed in North Korea, says a long-awaited UN report.
A panel of experts mandated by the UN's Human Rights Council said North Koreans had suffered "unspeakable atrocities", and that those responsible, including leader Kim Jong-un, must face justice.
The panel heard evidence of torture, political repression and other crimes.
Pyongyang refused to co-operate with the report and rejects its conclusions.
The UN commission said Mr Kim had failed to respond to an advance copy of the report, and a letter which warned him he could be held personally responsible for abuses.
Testimony given to the panel from defectors included an account of a woman forced to drown her own baby, children imprisoned from birth and starved, and families tortured for watching a foreign soap opera.
Michael Kirby, chairman of the independent Commission of Inquiry, said the report "calls for attention from the international community".
"At the end of the Second World War so many people said 'if only we had known... if only we had known the wrongs that were done in the countries of the hostile forces'," he said.
"Well, now the international community does know... There will be no excusing of failure of action because we didn't know," he said, at a news conference at UN headquarters in Geneva.
"Too many times in this building there are reports and no action. Well this is a time for action."
The BBC's Imogen Foulkes in Geneva says the report is one of the most detailed and devastating ever published by the United Nations.
The "gravity, scale and nature" of the allegations "reveal a State that does not have any parallel in the contemporary world", it says.
The report says that in North Korea:
- there is "an almost complete denial of the right to freedom of thought, conscience and religion" in North Korea
- "entrenched patterns of discrimination", rooted in the state-assigned class system, affect every part of life
- discrimination against women is "pervasive in all aspects of society"
- the state "has used food as a means of control over the population" and deliberately blocked aid for ideological reasons, causing the deaths of "hundreds of thousands" of people
- "hundreds of thousands of political prisoners" have died in "unspeakable atrocities" in prison camps in the past 50 years
- security forces "systematically employ violence and punishments that amount to gross human rights violations in order to create a climate of fear"
"In many instances, the violations of human rights found by the commission constitute crimes against humanity," says the report.
"These are not mere excesses of the state; they are essential components of a political system that has moved far from the ideals on which it claims to be founded."
The UN "must ensure that those most responsible for the crimes against humanity" are held accountable, through a referral to the International Criminal Court, or a UN tribunal.
The UN should also adopt targeted sanctions "against those who appear to be most responsible for crimes against humanity", says the report, and increase its monitoring of rights abuses in North Korea.
North Korea declined to participate in the panel's investigation, and said it "categorically and totally rejects" the findings.
Its response came in a two-page statement sent to Reuters from its diplomatic mission in Geneva.
"The DPRK [North Korea] once again makes it clear that the 'human rights violations' mentioned in the so-called 'report' do not exist in our country."
Mr Kirby said there was "a very good way to answer the many charges and complaints - and that is to allow the door to be opened" to the international community so they could see the situation for themselves.
Although this information has been in the public domain for years, the panel's inquiry is the highest-profile international attempt to investigate the claims.
South Korea welcomed the report, saying it hoped it would "raise the international community's awareness", while the US said it "clearly and unequivocally documents the brutal reality" of the Pyongyang regime.
However China, North Korea's only ally, said it would "not help resolve the human rights situation".
The panel will formally present its findings next month, when the Human Rights Council will decide which recommendations to support.
But it remains unclear what action will result. Correspondents say China would be likely to block any attempt to refer the North to the International Criminal Court.
An ad-hoc tribunal, like those set up for Rwanda, Sierra Leone or Cambodia, would appear unlikely without co-operation from elements within the country.