South Korean analysts suggest that Mr. Jang’s reported fall from grace might have been a power play by Mr. Kim, following a pattern set by his father and grandfather, who frequently shuffled aides to keep them from acquiring too much influence.

But other experts say reports that two of Mr. Jang’s aides were recently executed suggest his downfall might be tied to corruption in departments he controlled.

On Friday, the South Korean intelligence chief said that the two confidants were most likely punished for “financial issues, such as the pocketing of foreign currency,” said Jeong Cheong-rae, a lawmaker designated by the intelligence committee to brief the news media. A group of the elites was forced to watch the executions as a warning, Mr. Jeong quoted the spy chief as saying.

The lawmaker said Mr. Jang and his aides might have been involved in managing the huge secret funds the ruling Kim family is believed to have accumulated to help finance its missile and nuclear weapons programs and to import luxury goods to curry loyalty among the elite.

Mr. Nam’s briefing on Friday came after some South Korean news media outlets raised questions about the veracity of his agency’s report on the fate of Mr. Jang. Government critics suspect that the spy agency may be exaggerating its intelligence to divert public attention from a continuing investigation into allegations that its officers ran an online smear campaign against the rivals of President Park Geun-hye ahead of her election.

Analysts are waiting to see whether Mr. Jang will show up for a state ceremony on Dec. 17, the second anniversary of the death of Mr. Kim’s father, Kim Jong-il. If he does and the North Korean state news media identifies him with his titles, it could indicate that the news of his ouster is wrong, although the experts cautioned that North Korea might stage an appearance to try to hide signs of instability. As of Friday night, North Korea had issued no comment on the South Korean reports about Mr. Jang.