North Korean security chiefs and possibly even Supreme Leader Kim Jong Un himself should face international justice for ordering systematic torture, starvation and mass killings bordering on genocide, U.N. investigators said on Monday.

The investigators told Kim in a letter they were advising the United Nations to refer North Korea to the International Criminal Court (ICC), to ensure any culprits "including possibly yourself" were held accountable.

North Korea said it "categorically and totally" rejected the investigators' report, which it called "a product of politicization of human rights on the part of EU and Japan in alliance with the U.S. hostile policy."