However, Mr. Kim exercised power via a higher body, the National Defense Commission (NDC), of which his official title was chairman.
The NDC is composed of the army chief of staff, the defense minister, a vice marshal and Mr. Chang, the husband of Kim Kyong-hui, Mr. Kim’s sister.
Yet with his father having implemented the “Songun” (“Military First”) policy, which granted the armed forces massive privileges over the party and other sections of society, Kim Jong-un may be sitting on a powder keg as factions line up.
Kim Il-sung was a proponent of “Juche,” or self-reliance, which was the founding ideology of the regime. After his father’s death, Mr. Kim shifted to “Songun” as a way to keep the army happy and maintain his own grip on power, said John Tkacik, who served as chief of China intelligence at the State Department in the Clinton administration.
Mr. Tkacik said a showdown between the army and the internal security apparatus under Mr. Jang is likely in a matter of months.
“The military is too powerful. It competes with the party and is involved with confrontation with the U.S. and South Korea, so there might be conflict with the party,” said Choi Jin-wook, senior North Korea researcher at Seoul’s Korea Institute of National Unification. “If that happens, it would be very dangerous.”
Regional analysts expect the riskiest period to be 2012, which is the year Mr. Kim promised that his country would become a “great and prosperous nation.”
“In three to six months, there is the possibility of a factional struggle, depending on how much Chang and Kim Kyong-hui want to keep Kim Jong-un as a figurehead,” said Kim Byung-ki, a security specialist at Korea University.
North Koreans mourned the death of their “Dear Leader.” State media eulogized Mr. Kim as a “great master of politics and illustrious commander born of heaven,” and state TV showed people weeping.
Kim Jong-un is chairman of the funeral arrangements, according to North Korean media reports.
The roles given to the army, the Korean Workers’ Party and the reserve army under Kim Jong-un’s uncle, Mr. Chang, at the funeral services will provide a clue as to the transition of power, according to Western officials and analysts.
Meanwhile, South Korean President Lee Myung-bak spent Monday presiding over a Security Council meeting and a Cabinet meeting while the armed forces went on emergency alert.
The South Korean stock market, which usually shrugs off North Korea’s nuclear tests, missile launches and military attacks, sank 3.7 percent.
• Ashish Kumar Sen reported from Washington.