NEW YORK/SEOUL -- Amid mixed reports about the health of North Korean leader Kim Jong Un, speculation is brewing over the question of who might assume power in Pyongyang should he be incapacitated, with his 32-year-old sister emerging as a leading candidate.
While there has been no clear evidence that Kim is indeed ill, the U.S. intelligence community will no doubt be accelerating its information-gathering on the sibling, Kim Yo Jong, said Bruce Klingner, who spent 20 years working at the Central Intelligence Agency and the Defense Intelligence Agency and is now senior research fellow for Northeast Asia at the Washington-based Heritage Foundation think tank.
Klingner said that the CIA carries out "leadership analysis," separate from a more general "political analysis" of a country, where it tries to gain a deeper understanding of top leaders.
"The CIA is responsible for collecting files on the Kim family. It is not just factual information but also on each individual's behavior," Klingner said. He noted that such issues as medication history, drug abuse, temperament, self-confidence and tendencies for impetuous action would be standard traits to analyze.
"The CIA will be looking at how much influence Kim Yo Jong has and how officials are deferring to her," he said.
Her appearance at the Winter Olympics held in Pyeongchang, South Korea, in February 2018, gave the intelligence community an inside look at her standing within the leadership, according to Klingner. "Officials who were more senior than her in rank were clearly deferring to her," he said.
But Klingner also described North Korea as one of the hardest targets to obtain information on. "When I shifted from covering the Soviet Union to North Korea, the Soviets looked like an open book compared to Pyongyang," he recalled.
The South Korean government's insistence that nothing is amiss has failed to dispel rumors fueled by a CNN report last week that Kim was in "grave danger."
South Korea Unification Minister Kim Yeon-chul told a closed-door forum that South Korea has "enough intelligence to confidently say that there are no unusual developments" in rival North Korea that would back up speculation about Kim's health, his ministry said Monday.
"Kim Jong Un is alive and well," Moon Chung-in, foreign policy adviser to President Moon Jae-in, told Fox News on Sunday. "He has been staying in the Wonsan area since April 13."
Yet a number of diplomatic sources in South Korea have indicated it is highly likely that Kim is suffering from health problems of some kind.
The Kim dynasty derives its legitimacy from the "Mt. Paektu bloodline" -- the family lineage that directly links Kim Jong Un and his siblings to founding father Kim Il Sung. If Kim Jong Un cannot lead, experts believe the most likely scenario is a shift to a collective leadership system centering on Kim Yo Jong, the de facto No. 2.
A favorite of her late father, Kim Jong Il, Kim Yo Jong has long been groomed for power by North Korean propaganda master Kim Ki Nam, according to the Financial Times.
Her global profile grew significantly when she was sent to the Winter Olympics, becoming the first member of the ruling Kim family to visit the South since the Korean War. She also accompanied her brother to Singapore in 2018 and then to Vietnam the following year for Kim Jong Un's two summits with U.S. President Donald Trump.
Kim Yo Jong has been solidifying her power of late. She was reinstated as an alternate member of the Politburo of the ruling Workers' Party on April 11 and is believed to have recently been moved to a position overseeing party appointments and intelligence-gathering. But some see her facing challenges in maintaining a firm grip on the military.
Some observers see authority being handed to Kim Jong Un's uncle, Kim Pyong Il. The 65-year-old -- the younger half-brother of Kim Jong Il -- previously served as North Korean ambassador to the Czech Republic and returned to his home country for the first time in more than three decades late last year.
Kim Jong Un's three children are too young to take over directly, with the oldest being only 10. His older brother, Kim Jong Chul, was passed over for leadership and has remained out of the circles of power in Pyongyang.
Reuters reported Friday that China had sent a medical team to the North to provide advice, citing three people familiar with the situation, which would back up reports that Kim had undergone cardiovascular surgery.
Supporting the Reuters report, Washington-based 38 North, a North Korea monitoring group, on Saturday released an analysis of commercial satellite imagery showing a train believed to belong to Kim at a railway station in Wonsan.
Meanwhile, Pyongyang has been muted in its response. Kim "sent thanks to the officials and working people for having rendered sincere assistance to the Wonsan Kalma coastal tourist area under construction," North Korea's state mouthpiece Rodong Sinmun said Monday. But official media have not directly confirmed his activities or those of Kim Yo Jong since April 12.
Amid this turmoil, South Korea held a ceremony Monday to launch the start of a planned North-South railway project, two years after a historic summit between Moon and Kim Jong Un. Construction is expected to begin in late 2021.
The Panmunjom Declaration signed by the two leaders at the 2018 summit called for relinking the countries by rail and road, among other goals including formally declaring an end to the Korean War. The lack of progress on implementing the declaration -- owing partly to a failed summit between Kim and Trump -- is said to have deepened Kim's distrust toward Seoul.
While a rail link between the two countries is impossible now because it would violate United Nations sanctions, Moon has expressed hope of resuming bilateral cooperation, saying that "we will figure out what we can do despite the sanctions and work ceaselessly to implement it."
Additional reporting by Sotaro Suzuki in Seoul.