SEOUL, South Korea -- Kim Jong Un, the 30-year-old leader of North Korea, came to power two years ago so inexperienced and untested that the reclusive government named his uncle as the North Korean equivalent of a regent to watch over him.
On Tuesday, the National Intelligence Service of South Korea reported that the uncle, Jang Song Thaek, had been stripped of his powers, apparently by the young leader he was supposed to supervise. It was the biggest in a series of purges, promotions and reshufflings of elites that seem to have remade the government in the image of its young leader, who inherited his title, and apparently techniques for keeping the government in control, from his father and grandfather.
The political changes, which were not announced by North Korea and could not be independently confirmed, follow a series of upheavals, especially within the military. U.S. intelligence officials and some outside analysts speculate that Mr. Kim is sidelining the stalwarts of his father, Kim Jong Il, and elevating a new set of generals and party officials who owe their loyalty only to him. But there are also hints, one U.S. intelligence official said, that "there was some kind of broader contest for control, which Jang lost, at least for now."
Early in the young Kim's tenure, U.S. intelligence assessments questioned whether he would have the staying power to remain in office, and said he was regarded by the North Korean military as spoiled and naïve.
Two years later those assessments are reversing. He is now seen as fully in charge. Mr. Kim has already begun testing the loyalty of top officials by dismissing or demoting them and letting them try to win his favor again -- often by spying against others, another technique of leadership inherited from his father, according to South Korean officials and analysts.
Mr. Jang's apparent fall from power came after his two deputies at the administrative department of the ruling Workers' Party of Korea were executed last month on charges of "corruption and anti-party activities," according to South Korean lawmakers who were briefed by intelligence officials in a hurriedly scheduled meeting at the National Assembly in Seoul.
The intelligence agency did not reveal how it learned of the executions, the lawmakers said.
"I don't think Jang's deputies were executed for mere corruption. Rather, they were executed because they established a 'power,'" said Cheong Seong-chang, a senior analyst at Sejong Institute in South Korea.
Despite initial hints that Mr. Kim might seek a more cooperative relationship with the country's neighbors and the United States, he has accompanied political changes at home with a hard-line nationalistic policy of accelerating the country's nuclear program, the main card it has to play in international negotiations.
In February, North Korea conducted its third nuclear test, and it appears to be restarting its capacity to produce plutonium, a main ingredient for its small nuclear arsenal. And it has threatened to attack Japanese, South Korea and U.S. targets, though in recent months the country's warnings of imminent war have quieted.
The reported downfall of Mr. Jang, effectively North Korea's No. 2 leader, set off a frenzy of speculation among North Korea watchers and South Korean government officials. Since Mr. Kim took power, they have theorized that a power and policy struggle might be playing out behind the public displays of mass solidarity. Mr. Jang's rise in power in the past few years coincided with the humiliation of the old military elite, who surrendered some of their lucrative rights to trade in minerals and seafood to the Cabinet and the party, where Mr. Jang has built his career.
Some analysts said they feared that the eclipse of Mr. Jang so early in Mr. Kim's rule could suggest a power struggle that could destabilize the North. If so, they worry that Mr. Kim might resort to militaristic provocations to divert attention from domestic instability.
On Tuesday, the Defense Ministry in Seoul said it saw no unusual movement from the North Korean army.