Kim Jong Il, the North Korean leader who threatened the world with his nuclear weapons ambitions and suppressed his own people with imprisonment and isolation, left in the wake of his death Saturday an antiquated country with a power vacuum.

Kim’s death raises immediate questions about the future — and the stability — of perhaps the world’s most isolated state, which for six decades has been held together by the Kim family personality cult. Kim was deified by state media, described as the “Dear Leader.” A weeping television anchor Monday told North Korea of Kim’s death.

Security analysts and officials from Seoul to Washington have long believed that Kim’s death would double as a pivot point on the Korean Peninsula. But that poses a threat of its own, as North Korea tries to pass power to Kim’s youngest son, Kim Jong Eun, who is in his 20s.

In an announcement Monday, North Korea called Kim Jong Eun a “great successor” and urged its people to follow his leadership. The state also test-fired two short-range missiles off its east coast, according to South Korea’s Yonhap News Agency.

Yonhap quoted an official in Seoul as saying the test most likely was part of a routine drill and was not related to Kim Jong Il’s death.

Until late last year, the younger Kim had lived his life almost entirely behind a wall of privacy. But as his father struggled with his health, he accelerated a controversial power transfer and, in late September 2010, named Kim Jong Eun to several top military and political posts. This year, when the elder Kim made his customary visits to military camps and factories across the country, his son often accompanied him — not as an equal, but as a trainee.

One concern, described by numerous Korean security experts, is that the younger Kim could face opposition from more senior North Korean officials, including Jang Song Thaek, who had been acting as a caretaker for the transition. In recent years, Kim Jong Il tried to minimize the power of other older party members, often demoting them — sometimes even banishing them to the countryside — so they wouldn’t form allies of their own.

Since taking over from his father, Kim Il Sung, in 1994, Kim kept a tight hold on North Korean society, using the “juche” ideology — emphasizing national self-reliance to rationalize strict crackdowns on political opposition. Those who spoke out against the Kim family were sent to prison camps, defectors say, along with their parents and children.

The country’s leadership maintained a ban on most communication: Most North Koreans, even now, have no access to the Internet. Several hundred thousand North Koreans now have cellphones, but they can make only domestic calls.

As a result, North Korea dealt with almost no dissent — a stark contrast to Arab countries that this year revolted against authoritarian rulers. For almost two decades now, North Korea has defied predictions of its demise. Kim’s death sparked new concerns that the country could become less stable.

In Tokyo, Japanese leaders held an emergency security meeting. South Korea’s Joint Chiefs of Staff put its front-line military on emergency alert, with heightened concern about a provocation along the contested maritime border. Seoul’s stock market dipped more than 4.5 percent amid the news of Kim’s death.

In recent years, particularly since his apparent August 2008 stroke, U.S. intelligence agencies had monitored Kim’s health closely. But it was not clear whether they knew his death was imminent. Kim took several trips this year to China and Russia, traveling by heavily armored train.

Analysts at the CIA and other agencies have warned that his demise could destabilize the country and make it more dangerous.

“This brings extraordinary change and uncertainty to a country that has seen little change in decades,” said one U.S. official, who spoke on the condition of anonymity. “South Korea’s concern is warranted, frankly, because an insecure North Korea could well be an even more dangerous North Korea.”

For almost two decades, South Korea and the United States have discussed contingencies in the event of Kim’s death — and North Korea’s collapse. If the Korean Peninsula were to be unified, millions of impoverished North Koreans could flood the border into the South. The cost of unification, according to one major study, could exceed $1 trillion, and last year President Lee Myung-bak proposed a “unification tax” — not yet put into place — to prepare for such a moment.

The White House issued a statement late Sunday acknowledging Kim’s death: “The president has been notified, and we are in close touch with our allies in South Korea and Japan. We remain committed to stability on the Korean peninsula, and to the freedom and security of our allies.”

Secretary of State Hillary Rodham Clinton was briefed on the reports of Kim’s death, a department spokesman said.

Clinton has increased the pressure on the North Korean government in recent weeks, traveling to Burma last month in a bid to drive a wedge between Pyongyang and one of its few customers for nuclear technology. After the trip, there was speculation that she might follow her Burma visit with a trip to the North Korean capital. Clinton also appointed a new U.S. envoy last fall to make a new push for a diplomatic breakthrough on North Korea’s nuclear program.

Especially in the past two years, North Korea has depended for much of its security on China, which supplies Pyongyang with much-needed aid and investment. China has also used its influence to block U.N. measures against North Korea, and U.S. officials have called on China to use its influence to encourage North Korea’s liberalization.

Almost nothing is known about how Kim Jong Eun, if he successfully takes power, will run the country.

Before his death, Kim Jong Il had been grooming his third and youngest son as his successor. Kim Jong Eun studied for a time in Switzerland at a German-speaking high school in Liebefeld, a suburb of the Swiss capital, Bern. Former classmates remember a shy but determined boy obsessed with American basketball and expensive sports shoes. They say he spoke passable German and made some local friends but was monitored closely by staff members s from the North Korean Embassy in Bern.

He vanished in the middle of the school year in 2000, apparently to return to Pyongyang, and had not been seen in public since until he emerged at his father’s heir apparent last year. A campaign of hagiographic propaganda hailed him as the “Dear Young General,” but it is unclear how much support he has within the armed forces or the ruling party, both of which are dominated by far older men. His mother, a former dancer, died in 2004.

Staff writers Greg Miller and Joby Warrick in Washington and staff correspondent Andrew Higgins in Hong Kong contributed to this report.