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Kim Jong Un was so angry about his failed summit with Donald Trump in Hanoi in February that he executed his special envoy to the U.S. shortly after, a South Korean newspaper reported Friday.

The Chosun Ilbo newspaper, citing a source inside North Korea, reported that Kim Hyok Chol, along with four foreign ministry officials who were involved in preparations for the Vietnam summit, were executed by firing squad at Mirim airport in a suburb of Pyongyang in March.

Kim reportedly charged Chol with spying for the U.S., claiming he was “won over by the American imperialists to betray the supreme leader.”

The paper also reports that Kim’s top aide, Kim Yong Chol, has been sent to a forced labor camp in a remote northern region. Chol had visited the White House on a number of occasions, including personally delivering a “very nice” appreciation letter to Trump from Kim.

Kim was reportedly left embarrassed in Hanoi after Trump walked away from the negotiating table over North Korea’s demand that the U.S. lift all sanctions against Pyongyang.

The report has not been verified by any other media outlet, and officials in Seoul and Washington are yet to respond to the reports. According to the Wall Street Journal, South Korean officials said Friday they were investigating the report.

Earlier this month, when asked about rumors of executions of senior officials, U.S. Secretary of State Mike Pompeo told ABC that “it does appear that the next time we have serious conversations that my counterpart will be someone else.”

While there has been no official confirmation from Pyongyang, there were ominous signs coming from the secretive kingdom on Thursday.

An editorial in the Rodong Sinmunthe the official newspaper of the North’s ruling Workers’ Party, warned about “anti-party, anti-revolutionary acts” by officials who “pretend to work for the supreme leader in his presence but secretly harbor other dreams behind his back.”

“Such characters won’t escape the stern judgment from the revolution,” the editorial added.

North Korea watchers are divided about whether or not the report is likely to be accurate.

“I think the world should be very cautious regarding South Korean media’s reports of executions of high level North Korean officials,” Baohui Zhang, director of the Centre for Asian Pacific Studies at Lingnan University in Hong Kong, told VICE News.

“I think the world should be very cautious regarding South Korean media’s reports of executions of high level North Korean officials.”

“There are many instances that these people later resurfaced in public. North Korea is a totally secretive society and it is unlikely that a South Korean newspaper somehow gained detailed information on the latest executions,” Zhang said.

Other skeptics noted that trying to accurately predict Trump’s thinking, and in particular his decision to walk away from the negotiating table, would have been almost impossible ahead of the summit.

“If this is true, I would be surprised,” Tong Zhao, a North Korea expert at the Carnegie-Tsinghua Center for Global Policy in Beijing, told VICE News. “People have been executed because of disloyalty. But executing people because they tried but failed to do a good job?”

Still, others point out that executing officials at or near the top of the government is not unusual for Kim or his predecessors.

Robert Kelly, an expert in international relations at Pusan National University in South Korea, said he would “absolutely not” be surprised if the report turned out to be true. John Hemmings, Asia Director at the Henry Jackson Society, a British foreign policy think tank, told VICE News the report is “credible.” After the meeting ended, Hemmings pointed out, Kim had “60 hours to brood about the failure of the summit as his train made its way back to Pyongyang.”