An authoritative source familiar with U.S. intelligence reporting said on Monday it was entirely possible Kim had disappeared from public view to avoid exposure to COVID-19 and the sighting of his presidential train in the coastal resort area of Wonsan did suggest he may be there or have been there recently.
But the source said that since there was no authoritative backing for such a conclusion, U.S. agencies were also still considering the possibility Kim might be ill, even seriously.
38 North, a Washington-based North Korea monitoring project, said on Saturday that satellite images from last week showed a special train that was probably Kim's at Wonsan, lending weight to reports he had been spending time in the resort area.
While North Korean state media have not reported on Kim Jong Un's whereabouts since he presided over a meeting on April 11, they have carried near-daily reports of him sending letters and diplomatic messages.
That suggests that he is still carrying out his duties, Unification minister Kim said, although some experts say they are not necessarily conclusive.
"I agree with the South Korean government's assessment that there is no reason to think Kim Jong Un is not performing his duties," said Rachel Minyoung Lee, a former North Korea open source intelligence analyst for the U.S. government. "That said, I would not read too much into letters signed by Kim Jong Un. I would guess that most of them are not written by him anyway."