PYONGYANG, North Korea — Streams of mourners, some wailing and some grim-faced, placed flowers at monuments around the North Korean capital Tuesday in memory of longtime ruler Kim Jong Il, while state media hailed Kim's son and heir apparent as a man "born of heaven" — suggesting the transition to a new leadership was firmly on track.
Kim's death and the possibility of a power struggle in a country armed with nuclear weapons and known for its unpredictability has heightened tensions in the region.
President Barack Obama agreed by phone with South Korean President Lee Myung Bak to closely monitor developments. Japan's government also said it was being vigilant for any "unexpected developments."
South Korea's military has been put on high alert, and experts warned that the next few days could be a crucial turning point for the North, which though impoverished by economic mismanagement and repeated famine, has a relatively well-supported, 1.2 million-strong armed forces.
With an 11-day mourning period in effect for Kim, who died Saturday, flags flew at half staff and shops were closed to allow North Koreans to pay their last respects to the "Dear Leader," as he was called.
"Today, as well as yesterday, the Korean people have been coming here to Mansu Hill in deep sorrow at the loss of the benevolent father of our nation with the infinite feeling of longing," said Ri Ho Il, a lecturer at the Korean Revolutionary History Museum. "Our General (Kim Jong Il) is our people's benevolent father. He defended our people's happiness, carrying on his forced march both night and day."
Kim died of a massive heart attack brought about by overwork and stress, according to the North's media. He was 69 — though some experts question the official accounts of his birth date and location. The state funeral is to be held on Dec. 28.
North Korean officials say they will not invite foreign delegations and will allow no entertainment during the mourning period.
North Korean state media have given clear indications that Kim's third son will succeed him.
The Korean Central News Agency on Tuesday described Kim Jong Un as "a great person born of heaven," a propaganda term only his father Kim Jong Il and his grandfather Kim Il Sung had enjoyed. The Rodong Sinmun, the newspaper of the ruling Workers' Party, added in an editorial that Kim Jong Un is "the spiritual pillar and the lighthouse of hope" for the military and the people.
It described Kim, who is in his 20s, as "born of Mount Paektu," one of Korea's most cherished sites and Kim Jong Il's official birthplace. On Monday, the North said in a dispatch that the people and the military "have pledged to uphold the leadership of comrade Kim Jong Un" and called him a "great successor" of the country's revolutionary philosophy of self-reliance.
Whether the transition would be a smooth one remained an open question, however.
"The situation could become extremely volatile. What the North Korean military does in the next 24 to 48 hours will be decisive," said Bill Richardson, a former U.S. ambassador to the United Nations who has made several high-profile visits to North Korea.
Kim was in power for 17 years after the death of his father, the charismatic founder of the North Korean nation.
His death could set back efforts by the United States and others to get Pyongyang to abandon its nuclear weapons ambitions. It also comes at a sensitive time for North Korea, which is preparing for next year's 100th anniversary of the birth of Kim Il Sung.
Concerns are high that Kim Jong Un — being young and largely untested — may feel he needs to prove himself by precipitating a crisis or displaying his swagger on the international stage.
North Korea conducted at least one short-range missile test Monday, a South Korean official said. But South Korea's military sees the firing as part of a scheduled routine drill, instead of a provocation, the official said, speaking on condition of anonymity because of a policy that bans commenting on intelligence matters.
Some analysts, however, said Kim's death was unlikely to plunge the country into chaos because it already was preparing for a transition. Kim Jong Il indicated a year ago that Kim Jong Un would be his successor, putting him in high-ranking posts.
South Korea's president urged his people to remain calm while his Cabinet and the Parliament convened emergency meetings Tuesday. Unification Minister Yu Woo Ik said his government is refraining from moves that may exasperate North Korea.
The Defense Ministry said the South Korean military and the 28,500 U.S. troops stationed in South Korea had bolstered reconnaissance and were sharing intelligence on North Korea.
The White House said in a statement that it is closely monitoring reports of Kim's death. The Obama administration may postpone decisions on re-engaging the North in nuclear talks and providing it with food aid, U.S. officials said.
The administration had been expected to decide on both issues this week, possibly as early as Monday, but the officials said Kim's death would likely delay the process.