North Korea executed its former top nuclear envoy with the U.S. along with four other foreign ministry officials in March after a failed summit between Kim Jong Un and Donald Trump in Vietnam, South Korea’s Chosun Ilbo newspaper reported.

Kim Hyok Chol, who led working-level negotiations for the late-February summit in Hanoi, was executed by firing squad after being charged with espionage for allegedly being co-opted by the U.S., the newspaper said, citing an unidentified source. The move was part of an internal purge Kim undertook after the summit broke down without any deal, it said.

Previous reports in South Korea media about senior North Korean officials being executed have proven false.

Speculation has swirled for months about the fate of Kim Hyok Chol, who hasn’t received any mentions in state media reports.

Talks between the U.S. and North Korea have stalled since the Vietnam summit, with no plans for them to get underway.

Stephen Biegun, the Trump administration’s nuclear envoy to North Korea and Kim Hyok Chol’s counterpart, plans to meet with Japanese and South Korean negotiators this weekend in Singapore.

The February summit in Hanoi abruptly collapsed, with Trump calling off the talks. Analysts said Kim may have overplayed his hand by seeking too much sanctions relief and offering too few nuclear disarmament steps in return.

A career diplomat known for his expertise in nuclear deterrence against the U.S., Kim Hyok Chol’s appointment earlier this year as Biegun’s counterpart surprised North Korea watchers. One South Korean TV outlet drew a circle around him in a video from a White House meeting between Trump and North Korean officials, asking who he was.

Kim Jong Un’s top aide Kim Yong Chol is reportedly undergoing hard labor, according to the South Korean newspaper report.