North Korea announced this week that leader Kim Jong Un's uncle by marriage, Jang Song Thaek, was executed, and now analysts are trying to figure out the motive behind the unexpected move.

SEOUL -- The once-powerful uncle of North Korean leader Kim Jong Un was  sentenced to death and executed Thursday, the state Korea Central News Agency reported Friday.

The execution of Jang Sung Taek, 67, came only four days after he was accused of "anti-state, counter-revolutionary activities," stripped of all his posts and arrested at a politburo meeting of the ruling party. The 30-year-old North Korean leader allegedly presided over the meeting.

Though Jang's fall from grace was already clear, observers of the reclusive nation had speculated that he would not be executed because he was the husband of Kim Kyoung-hui, the sister of the current leader's father and predecessor, Kim Jong Il.

PHOTOS: North Korean leader Kim Jong Un

U.S. intelligence officials said they could not confirm the execution but have no reason to doubt the reports.

"It is quite shocking, but it seems like Kim Jong Un was determined to show whoever challenges his sole leadership will be punished, without mercy," Kim Yong Hyun, a North Korea studies professor at Dongguk University told South Korean news channel YTN.

The North Korea studies professor said the timing of the execution, which came five days before the second anniversary of the death of Kim Jong Il, seem to confirm that the era of Kim Jong Un had truly begun.

Despite the turmoil, former NBA star Dennis Rodman, who has built a friendship with Kim, was scheduled to visit the communist state next week. Quoting sponsors of the event, Agence France-Presse news service reported  Friday that Rodman is organizing a friendship exhibition game between North Korea and a team of mainly ex-NBA players for Jan. 8, Kim's birthday.

Paddy Power, an Irish bookmaker and sponsor of the event, told AFP that the match will not be affected by the recent internal political events of North Korea.

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Choi is a special correspondent.