North Korean officials making a rare appearance at a United Nations human rights event on Wednesday laughed among themselves at the testimony of former labor camp detainees and referred to the ambassador of Botswana with derogatory racial language, according to Korean-speaking sources who overheard their conversations and spoke with VICE News.

The special session featured an awkward and testy exchange between Kim Ju Song, advisor for political affairs at the Democratic People's Republic of Korea's mission to the UN, and Michael Kirby, the retired Australian judge who headed a recent UN commission of inquiry into North Korean human rights abuses. The commission released a report in March that cited forced labor, starvation, persecution of religious believers, and a massive network of political prisons holding up to 120,000 people among various violations and crimes against humanity committed by North Korea's government.

Speaking along with Kirby were the ambassadors of Australia, Panama and Botswana — whose delegations co-sponsored the hearing — as well as two former North Korean detainees whose experiences were featured in the commission's report.

At one point, members of the North Korean delegation were heard referring to Botswana's UN Ambassador Charles Ntwaagae in Korean as "that black bastard," sources who were nearby told VICE News. They also chuckled at the testimony of Kirby and the two prison escapees, Jung Gwang-il and Kim Hye Sook. Those in the room with the North Korean delegation who later spoke with VICE News insisted on anonymity due to fear of reprisal.

"I am not the least bit bothered by whatever insult they may have hurled at me," Ambassador Ntwaagae told VICE News when approached for comment. "What is important is everyone recognizes the report of the commission of inquiry makes grim reading. What is important is that they are challenged to rebut the findings of the report."

North Korea's government, said Ntwaagae, is unable to contradict Kirby and the testimony given by the victims. Botswana broke off diplomatic relations with North Korea following the report's publication.

"It behooves the DPRK to urgently put its governance house in order with a view to engage and create democratic space for dialogue and inclusivity, as well as respect for the rule of law and human rights of its own people," he added.

The derogatory remarks weren't the first made by North Koreans in the context of the inquiry.

In April, a commentary published in North Korea's Central News Agency called Kirby — who is openly gay and has advocated for LGBT rights — "a disgusting old lecher with a 40-odd-year-long career of homosexuality."

"It is ridiculous for such gay to sponsor dealing with others' human rights issue," the Central News Agency item said.

In September, North Korea released a 53,000-word report on their own human rights system, which they called "the world's most advantageous." The document's authors also referred to witnesses like Ms. Kim and Mr. Jung as "human scum."

On Wednesday, Kirby repeatedly asked Mr. Kim to retract the "human scum" comment. Kim doubled down instead, calling the report "groundless" and claiming that the two escapees had been coaxed into providing testimony as part of a "political conspiracy of the United States and hostile forces in their attempt to overthrow our political and social system."

The "human rights violations mentioned in the commission of inquiry report cannot be allowed to exist in my country, where the rights and freedom of our people are formally guaranteed," argued Mr. Kim.

Prior to their testimony, a North Korean official approached Mr. Jung and Ms. Kim with a recording device and appeared to videotape them both. Given that the hearing was being publicly broadcast over the UN's television network and would be made available hours later online, the move was seen by many in the room as blatant intimidation.

"They were taking photos and recording videos," Ms. Kim complained to reporters after the session through an interpreter. She still has family in North Korea, and expressed concern for their welfare. "They cannot kill me. Maybe there will be more moments of suffering for my family."

Kim first entered a labor camp at the age of 13, where she would remain for 28 years. Half of that time was spent working in a coal mine, an experience that left her with chronic lung ailments.

"We ate grass so much," she said. "We collected acorns to survive."

"The number one rule was you shouldn't ask why you were there," she went on. "Many people were publicly executed for that."

Param-Preet Singh, senior counsel at Human Rights Watch's international justice program, attended the hearing and later told VICE News that the mere presence of North Korean officials was meant to threaten witnesses, particularly given their intransigence on matters of human rights.

"The whole point is to show how they intimidate ordinary people," said Singh. "What's frustrating for them is they have these witnesses who refuse to be intimidated by them."

The hearing came amid escalating pressure from North Korea on member states following the introduction of a joint European Union-Japan General Assembly resolution rebuking the hermit kingdom for its record of abuses. The Europeans and Japanese are seeking targeted sanctions and a referral of North Korea's government to the International Criminal Court. That would require a vote in the Security Council, where China would be expected to exercise its veto power to block an investigation at The Hague.

Not to be outdone, North Korea last week introduced its own draft resolutions in the UN calling for an end to human rights inquiries directed at specific countries.

Its government has also sent emissaries to South Korea, the European Union, and Washington in an attempt to influence discussions of its human rights record. On Tuesday, North Korean officials released American prisoner Jeffrey Fowle, reportedly on the order of supreme leader Kim Jong-un.

On Wednesday, Kirby called North Korea's sudden interest in diplomacy and the freeing of Fowle part of a "charm offensive."

"This is the moment of truth, and it is extremely important that it should not be traded away for a little bit of charm," Kirby told reporters.

"A few honeyed words expressed in the last few weeks by the representative of North Korea facing the reality of the outrage of the international community hasn't improved one iota the position of human rights on the ground," he added.