In 2003, Kim Yong-soon, Kim Jong-il’s trusted adviser on relations with South Korea, died in a car accident.

Since 2001, Mr. Ri has been the No. 2 at the organization department, a party organ Kim Jong-il used to consolidate his power in the 1970s and is still believed to be heading. Mr. Ri was also a close confident of Ko Young-hee, Kim Jong-un’s late mother, according to officials and analysts in Seoul. Ms. Ko died in 2004.

“Kim Jong-un lost one of his two most important promoters, except his father,” said Cheong Seong-chang, another North Korea expert at Sejong Institute. The other is Jang Song-taek, Kim Jong-il’s brother-in-law and director of the administration department of the party.

Mr. Jang is said to have been in a long-running rivalry with Mr. Ri.

Mr. Jang’s influence has expanded in recent years as Kim Jong-il, who is believed to have suffered a stroke in 2008, has relied more heavily on close relatives, Mr. Cheong, the analyst, said.

Yoo Ho-yeol, a North Korea expert at Korea University, said the rivalry raised questions about whether Mr. Ri’s death was truly an accident, but Mr. Cheong said that if it had been an assassination, “the North would not have announced his death as quickly as they did.”

In any case, both of the experts agreed that Mr. Jang’s influence would rise further with Mr. Ri’s death. But they said that the death would not create any serious challenge to Kim Jong-un because his father had already rallied the country’s most influential political players behind his son. After the torpedo attack on a South Korean warship, which investigators from several countries recently said was carried out by North Korea, some analysts speculated that the North had acted to increase Kim Jong-un’s chances at succeeding his father by building support for him within the military.

The other top official to die recently was another first deputy director of the party’s organization department, Ri Yong-chol, 81, who the North reported had a heart attack in April.