The impoverished but nuclear-armed nation stands accused by United Nations investigators of "systematic, widespread and gross" human rights violations that range from rape, torture, extrajudicial killings to running political prisoner camps.
Pyongyang calls such accusations anti-regime propaganda.
But the issue was sidelined during Kim's summits last year with democratically-elected presidents Moon Jae-in of South Korea and Donald Trump of the US, who have focused on diplomacy and the North's nuclear arsenal.
A second meeting between Kim and Trump is expected soon, after which Kim could potentially travel to Seoul.
"It will be a missed opportunity if in 2019 human rights is not addressed by all the parties, including more importantly the government of DPR Korea," said Tomas Ojea Quintana, the UN special rapporteur on human rights in the North, using the North's official name.
The human rights situation remained "serious" in the isolated country, he told reporters in Seoul, despite last year's diplomatic developments.
The Argentine lawyer called on the South Korean government to engage more strongly with Beijing to stop forced repatriations of North Korean defectors caught in China, which views escapees as illegal aliens rather than refugees.
Returnees to the authoritarian state can face imprisonment and torture, according to campaigners and rights groups.
Asked whether South Korean officials were hesitant to raise rights with the North in their pursuit of dialogue, Ojea Quintana said Seoul officials told him improved inter-Korean relations would "further improve human rights" in the reclusive state.