Secretary of State Mike Pompeo offered a cautious response on Friday to a report that North Korean dictator Kim Jong-un had a top envoy executed after a failed summit with President Trump made him look bad.

“We’re doing our best to check it out. I don’t have anything else to add to that today,” Pompeo said while in Berlin for an official visit.

Kim Hyok-chol — who led talks with the US ahead of the February summit in Hanoi — was killed by firing squad in March at Mirim Airport in Pyongyang along with four Foreign Ministry officials after they were charged with spying for the US, South Korea’s Chosun Ilbo newspaper reported on Friday, citing an anonymous source.

“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 summit in Vietnam’s capital, the second between Kim and Trump, broke down over US calls for complete denuclearization of the Korean Peninsula and North Korean demands for sanctions relief.