The head of a UN inquiry into North Korea rights abuses said he was reduced to tears by witness accounts of people who fled the hardline state.
Michael Kirby, a veteran Australian high-court judge, said this week the treatment of women returned to North Korea after already being abused in China had been particularly tough.
Fewer North Koreans were getting out of the country, perhaps because of tighter border controls, another rights investigator said.
The UN Human Rights Council commission of inquiry has heard evidence in London, Tokyo and Seoul and was to begin hearings in Washington.
The inquiry has heard harrowing stories of labour camps in the isolated state ruled by Kim Jong-un as well from relatives of Japanese believed abducted by North Korean agents and families divided since the 1950-1953 Korean war.
"Some of the testimony has been extremely distressing," Kirby, who has also investigated abuses in Cambodia, said after addressing a UN General Assembly committee.
"I am a judge of 35 years' experience and I have seen in that time a lot of melancholy court cases which somewhat harden one's heart," he said.
"But even in my own case, there have been a number of the testimonies which have moved me to tears and I am not ashamed to say that.
"You would have be a stony-hearted person not to be moved by the stories that the commission of inquiry has received."
Kirby said the testimonies "should be seen and they should be considered for the follow up that will be required" by the UN system. All of the testimonies have been put online.
The inquiry leader said women "figure very greatly in testimony" and make up the majority of the North Koreans who have tried to flee. "Many of them have left and gone on to China where they are subject to forced marriages, trafficking and other human rights burdens," he said.
But China sends back many who are caught and those women "have suffered very grievously", Kirby said.
North Korea has condemned the UN inquiry as hostile and said the witnesses are liars.
Kirby said the inquiry, which will report to the Human Rights Council in March, had asked North Korea to send a representative who could question the witnesses.
Marzuki Darusman, the UN special rapporteur on North Korea who is also a member of the inquiry, said meanwhile that 1,041 North Koreans had arrived in South Korea in the first nine months of the year, against 1,509 people in all of 2012 and 2,706 people in 2011.
"This represents a reversal of the trend of steady increase in the number of annual arrivals since 1998, possibly due to recently tightened border control and increased incidents of refoulement," Darusman had written in a statement to the UN General Assembly.