North Korea executed its special nuclear envoy to the United States as part of a purge of senior officials over the failed summit between leader Kim Jong Un and President Donald Trump, South Korea's Chosun Ilbo newspaper claimed Friday.

Kim Hyok Chol was executed by firing squad in March along with four other foreign ministry officials, the paper reported, citing an unidentified North Korean source.

North Korea neither confirmed nor denied the report. South Korea's government was not able to confirm the claim. Previous media reports about the fate of North Korean officials who have fallen afoul of Pyongyang's leader have proven to be false.

Chosun Ilbo is one of South Korea's largest daily newspapers. However, it's notoriously difficult to get information out of North Korea because it closely guards secrets.

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Still, Chosun Ilbo reported Kim Hyok Chol and the other senior officials were shot after being accused of spying for the United States. The paper reported Kim Jong Un ordered the purge amid mounting dissatisfaction with the summit in Hanoi – the second time Kim and Trump met for face-to-face talks. In Vietnam, they failed to reach a deal because of conflicts over the White House's call for complete denuclearization of the Korean peninsula and North Korean demands for sanctions relief.

Since then, amid a diplomatic standoff between Pyongyang and Washington, North Korea has resumed testing short-range ballistic missiles, ending a pause in launches that began in late 2017. The tests are viewed as a way for Kim to pressure Trump to ease sanctions without actually causing negotiations to collapse.

"North Korea fired off some small weapons, which disturbed some of my people, and others, but not me," Trump tweeted during a recent trip to Japan.

Secretary of State Mike Pompeo was asked about the Chosun Ilbo report during a news conference in Berlin. He said Friday the U.S. was "doing our best to check it out."

If the report is confirmed it's not clear what, if any, impact it could have on Trump's faltering diplomatic efforts aimed at halting North Korea's nuclear weapons program.

"One more wrong move by either side could bring the entire house of cards tumbling down," wrote security analyst Ankit Panda in the South China Morning Post on Friday.

Panda said if negotiations break down completely, North Korea has a plan B.

"It is clearer than ever that Kim is setting up for a significant deepening of Russia-North Korea ties – all at the expense of the United State," he wrote in the opinion piece.

Kim and Russian President Vladimir Putin held their first ever talks in April.

Kim has presided over high-profile purges since taking over as North Korea's leader in 2011. Kim’s uncle, Jang Song Thaek, at the time North Korea’s second most powerful man, was convicted of treason and executed in late 2013. And Rodong Sinmun, a North Korean newspaper, appeared to indirectly refer to the purge on Thursday.

"Acting like one is revering the leader but dreaming of something else when one turns around, is an anti-party, anti-revolutionary act that has thrown away the moral fidelity towards the leader and such people will not avoid the stern judgment of the revolution," the paper said. "There are traitors and turncoats who only memorize words of loyalty towards the leader and even change according to the trend of the time."

Kim Yo Jong, the North Korean leader's sister, who regularly accompanies her brother at big events, has not been seen in public since the Hanoi meeting.

Chosun Ilbo also reported that Kim Yong Chol, Kim’s right-hand man and Pompeo’s counterpart at the Hanoi summit, has been sent to a labor and reeducation camp near the Chinese border. That claim, too, was not been independently verified.

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