The news was also broadcast on the radio, which was piped into the subway. People sat quietly and listened as the announcer listed Jang's crimes.
During his two years in power, Kim Jong Un has overseen nuclear and missile tests, other high-profile purges and a barrage of threats this spring, including vows of nuclear strikes against Washington and Seoul. In contrast, his father, Kim Jong Il, took a much lower public profile when he rose to power after the death of his father, Kim Il Sung, in 1994.
It's not clear what the execution and Kim Jong Un's very public approach to leadership says about the future of the country, which is difficult for outsiders to interpret. Some analysts see the public pillorying of such a senior official, and one related to the leader, as a sign of Kim Jong Un coming into his own, the final consolidation of power that began with his father's death.
"Whatever problems it faced, North Korea has usually acted in a way to bolster its leaders," said Chin Hee-gwan, a professor South Korea's Inje University. "By showing a little bit of a reign of terror, it's likely that Kim Jong Un's power will be further consolidated."
But others see signs of dangerous instability and a rare acknowledgement that behind the scenes, Kim Jong Un's rise has not been as smooth as previously thought.
"North Korea's announcement is like an acknowledgement that Kim Jong Un's government is still in a transitional period," said Lim Eul Chul, a North Korea expert at South Korea's Kyungnam University.
The execution could be followed by more purges, Lim predicted, but Kim Jong Un will eventually ease up in his approach to domestic affairs because he'll face a bigger crisis if he fails to revive the struggling economy and improve people's living standards.
There are fears in Seoul that the removal of Jang and his followers two of his aides were executed last month, South Korea's National Intelligence Service said could lead to a miscalculation or even attack on the South.
Top South Korean presidential security and government ministers held an unscheduled meeting Friday to discuss Jang's execution and its aftermath, according to the presidential Blue House. Seoul's Defense Ministry said the North Korean military has not shown any unusual activities and that there is no any suspicious activity at the North's nuclear test site and missile launch pads.
There are also questions about what the purge means for North Korea's relationship with its only major ally, China. Jang had been seen as the leading supporter of Chinese-style economic reforms and an important link between Pyongyang and Beijing.
Although the high-level purges over the last two years could indicate confidence, Victor Cha, a former senior White House adviser on Asia, said he sees signs of "a lot of churn in the system."
"If he has to go as high as purging and then executing Jang, it tells you that everything's not normal in the system," said Cha, an analyst at the Center for Strategic and International Studies think tank in Washington. "When you take out Jang, you're not taking out just one person you're taking out scores if not hundreds of other people in the system. It's got to have some ripple effect."
North Korea has recently turned to attempts at diplomacy with South Korea and the United States. But tensions have remained high since Pyongyang's threats in March and April, which included warnings that it would restart nuclear bomb fuel production.
There was no immediate word about the fate of Jang's wife, Kim Kyong Hui, the younger sister of Kim Jong Il, although some analysts believe that because she is directly related to the nation's founder, Kim Il Sung, and has been reportedly ill, she may be spared Jang's fate. She was also seen as an important mentor to Kim Jong Un after her brother's 2011 death.
The White House said that "if confirmed, this is another example of the extreme brutality of the North Korean regime."
The KCNA report was unusually specific in its accusations at times. For instance, it criticized Jang for not rising and applauding his nephew's appointment to a senior position because Jang "thought that if Kim Jong Un's base and system for leading the army were consolidated, this would lay a stumbling block in the way of grabbing the power."
One resident in Pyongyang, Kim Un Song, a doctor at a hospital, said she was surprised at the news but supported the execution.
"We trust and believe only in Marshal Kim Jong Un. Anti-revolutionary elements can't shake our faith. I don't know if there are more out there, but they will never shake our faith," she said. "It's very good that he was executed."
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Klug reported from Seoul, South Korea. AP correspondent Hyung-jin Kim contributed to this story from Seoul.
