North Korea said that its top official on inter-Korean relations died in a traffic accident, in one of the highest-ranking deaths in Pyongyang since the execution of Kim Jong Un’s uncle two years ago.

Wednesday’s announcement of Kim Yang Gon’s death immediately led to speculation that the official had been purged, though the official media report lavished praise on him, calling him a “steadfast revolutionary comrade” and “the closest comrade-in-arms” of Kim Jong Un, noting that the North Korean leader would lead the funeral...