A UN official on Thursday said the focus on human rights in North Korea should not be lost amid the denuclearisation push, ahead of next week's U.S.-North Korea summit in Singapore.

Tomas Ojea Quintana, UN Special Rapporteur on the Situation of Human Rights in the Democratic People's Republic of Korea, told reporters in Geneva on Thursday that North Korea is struggling with a lack of food and that some 10 million people there are in need of humanitarian aid.

He praised the release of three US citizens in May who had been held in Pyongyang for more than a year, saying that "there is no rule of law in the DPR Korea, therefore these people were under arbitrary arrest".

Ojea Quintana called for North Korean leader Kim Jong Un to declare a general amnesty for political prisoners, to send "a very important signal."