A major UN investigation into human right abuses in North Korea is set to conclude that the country has committed crimes against humanity and should be referred to the international criminal court in the Hague, according to reported leaks of its findings.

The commission of inquiry on human rights in the country, set up in March by the UN's Human Rights Council, is due to announce its findings in Geneva on Monday. The Associated Press, quoting officials who had seen the commission's embargoed report, confirmed it found North Korea culpable for offences including crimes against humanity through starvation and extermination, as well as the abduction of people in South Korea and Japan.

The report concludes that the evidence gathered by the three-person commission, which held sometimes emotional public sessions in Seoul, Tokyo, London and Washington, gives "reasonable grounds … to merit a criminal investigation by a competent national or international organ of justice".

One part of the commission's remit was to decide whether North Korea's leadership, potentially including the top ruler, Kim Jong-un, should be referred to the ICC. While North Korea is not a signatory to the treaty that created the ICC, the Australian retired judge who heads the commission, Michael Kirby, has noted previously that the UN security council can extend the court's remit in exceptional cases.

However, any such move by the security council is likely to be vetoed by China, which has close links with North Korea and maintains a policy of sending back people found to have fled across the North Korean border into China, despite widespread evidence they face mistreatment and detention on return. Kirby has said the report is likely to hold China to account for this policy. North Korea has refused all requests to participate in the process.

Witnesses at the unprecedented public evidence sessions included escapees from North Korea who gave appalling accounts of life in prison camps, including claims one female prisoner was forced to drown her new-born baby and prisoners were put in a cell with a 50cm-high door, forcing them to enter by crawling.

In a recent interview with the Guardian, Kirby expressed regret that there was more media coverage of the curiosities of the dynastic Stalinist state's rulers, such as visits by the retired US basketball player Dennis Rodman, than of rights abuses.

"That is a commentary, really, on the international media," he said. "But it's also a commentary on the relatively closed nature of North Korea. It is a country which to some extent has been able to sail under the attention of the international community by being closed."

Even before the report was concluded, Kirby said evidence of some rights abuses was clear: "There are objective signs that are really uncontested. For example, in North Korea a third of infants up to their fifth year are severely stunted. That is an objective sign of failure of government to properly attend to the feeding of the population.

"If you have a closed society you can't really blame the general population for not knowing. But our duty is to bridge the gap, to shine a spotlight. That's what we're trying to do. One of the most powerful images viewed during the inquiry was that of the Korean peninsula at night. It shows the light in China and South Korea, and a large, dark section, which is North Korea. Well, our job is to shine a light into the dark section. That's exactly what we're going to do."