North Korea has executed the uncle of leader Kim Jong Un, who until recently was seen as one of Kim's chief advisers.
The official Korean Central News Agency says Jang Song Thaek was put to death Thursday after a facing a special military tribunal.
The report called him "a traitor to the nation for all ages who perpetrated anti-party, counter-revolutionary factional acts in a bid to overthrow the leadership of our party and state."
Jang was also accused of crimes, including corruption, womanizing and drug use.
Leonid Petrov, a Korea analyst at the Australian National University, says he doubts whether Jang was actually trying to overthrow the Kim government.
"I think it has nothing to do with what really happened. Jang Song Thaek was a loyal member of Kim's regime. He was appointed by Kim Jong Il to supervise his son. Jang Song Thaek was doing everything possible to promote Kim Jong Un's image."
Petrov says a personal or family dispute could have led to the execution. But he says it is also clear Kim viewed Jang as a threat, and that he felt the need to send a message that he is in complete control.
"The elites are scared to death at the moment. And the grassroots population of North Korea also gets the message that it is Kim Jong Un who is in the driver's seat, they must follow his orders and there's simply no alternative or any place for dissent in North Korea."
Other analysts say the move could reflect weakness on behalf of Kim Jong Un, who is trying to consolidate power following his father's death in late 2011.
There were no signs of instability or provocation in North Korea following the news. But South Korea's defense ministry said it is closely monitoring the North's military for aggressive movements.
South Korea's office of the president held an urgent national security meeting Friday to discuss the implications for stability on the Korean peninsula. A Unification Ministry spokesman said Seoul is watching the events in the North with concern.
The U.S. State Department says it can not immediately verify Jang's execution. But spokeswoman Marie Harf said U.S. officials have no reason to doubt it. If confirmed, Harf said the execution will serve as another example of the "extreme brutality" of the North Korean regime.
Jang was married to Kim Jong Un's aunt, Kim Kyong Hui, the sister of the late North Korean leader Kim Jong Il. Jang fell from grace in the past under Kim Jong Il when he disappeared for a few years only to return to a high rank just ahead of the leadership transition.