North Korea executed its nuclear envoy to the United States as part of a purge of officials who steered negotiations for a failed summit between leader Kim Jong-un and US President Donald Trump, a South Korean newspaper said on Friday. Kim Hyok Chol was executed in March at Mirim Airport in Pyongyang, along with four foreign ministry executives after they were all charged with spying for the United States, the <em>Chosun Ilbo</em> reported, citing an unidentified source with knowledge of the situation. "He was accused of spying for the United States for poorly reporting on the negotiations without properly grasping US intentions," the source was quoted as saying. The February summit in the Vietnamese capital of Hanoi, the second between Mr Kim and Mr Trump, failed to reach a deal because of conflicts over US calls for complete denuclearisation of the Korean peninsula and North Korean demands for sanctions relief. Reuters was unable to independently confirm the report. Previously, some North Korean officials have reportedly been executed or purged only to reappear with a new title. US State Department officials said they had no information to confirm the report. A spokeswoman at South Korea's Unification Ministry declined to comment. An official at the presidential Blue House in Seoul said it was inappropriate to comment on an issue that should first be verified. A diplomatic source told Reuters there were signs Kim Hyok Chol and other officials were punished for the breakdown of the summit, such as by being sent to a labour camp for re-education, but there was no evidence they were executed. Kim Yong Chol, Kim Jong-un's right-hand man and the counterpart of US Secretary of State Mike Pompeo before the Hanoi summit, had also been sent to a labour and re-education camp in Jagang province near the Chinese border, the <em>Chosun Ilbo</em> reported. Key officials who worked with Kim Yong Chol have been out of the public eye since the summit, while seasoned diplomats who previously appeared to have been sidelined, including vice foreign minister Choe Son Hui, were seen returning to the spotlight. A South Korean lawmaker told Reuters in April that Kim Yong Chol, a hawkish former spymaster, had been removed from a key party post. Kim Hyok Chol was seen as a rising star when he was appointed to spearhead working-level talks with US nuclear envoy Stephen Biegun weeks before the Hanoi summit. However, little was known about his expertise or the role he undertook during those talks. The other four allegedly executed alongside him included diplomats working on Vietnam relations, the <em>Chosun</em> report said. "This is a man who might provide some tactical advice to the leader but is otherwise a message bearer with little negotiating or policy-making latitude," said Michael Madden, a North Korea leadership expert at the Washington-based Stimson Centre. "Instead, they put in someone like Kim Hyok Chol to insulate Choe Son Hui and more substantive diplomatic personnel, to a certain degree he is expendable and his superiors are not." Among the penalised officials were Kim Song Hye, who led preparations as part of Kim Yong Chol's team, and Sin Hye Yong, a newly elevated interpreter for the Hanoi summit. They were said to have been detained in a camp for political prisoners, the newspaper said. The diplomatic source said Kim Song Hye's punishment seemed inevitable because she was a "prime author" of the North's plan to secure sanctions relief in return for dismantling the Yongbyon main nuclear complex. The idea was rejected by the United States demanding a comprehensive roadmap for denuclearisation. Kim Song Hye had also worked closely with Kim Yo Jong, the North Korean leader's younger sister and a senior party official whom Kim Song Hye accompanied to South Korea for the Winter Olympics last year. Kim Yo Jong was also lying low, the paper reported, citing an unidentified South Korean government official. Mr Madden, however, said Kim Yo Jong's status remained unchanged as Mr Kim's top aide, citing her attendance at key party meetings in April and appearance in state media reports. Ms Sin was charged with making critical interpretation mistakes that included missing an unspecified "last-minute offer" the North Korean leader supposedly made as Mr Trump was about to walk out, <em>Chosun</em> reported. North Korea's official party mouthpiece <em>Rodong Sinmun</em> warned on Thursday that "two-faced" officials would face the "stern judgment of the revolution". "It is an anti-Party, anti-revolutionary act to pretend to be revering the leader in front of him when you actually dream of something else," it said in a commentary. "There are traitors and turncoats who only memorise words of loyalty toward the Leader and even change according to the trend of the time," it said. The newspaper accused Jang Song Thaek, Mr Kim's uncle, of committing "anti-party, anti-revolutionary acts" after he was executed in December 2013. Hong Min, a senior fellow at the Korea Institute for National Unification in Seoul, said it was possible Kim Hyok Chol and other officials faced some penalty but further verification was needed. "Executing or completely removing people like him would send a very bad signal to the United States because he was the public face of the talks and it could indicate they are negating all they have discussed."