By Mark Bendeich
(Reuters) - North Korea's neighbors and its old enemy the United States appealed for stability on Monday after the death of leader Kim Jong-il plunged one of the world's most heavily militarized regions into fresh uncertainty.
China and Russia offered condolences and support for their ally's new leaders, while Western states expressed hope that a change in leadership could ease North Korea out of decades of extreme isolation and better the lives of its suffering people.
Kim suffered a heart attack while travelling on a train, North Korean state media said, setting up the autocratic, well-armed and nuclear-ambitious state for only its second leadership change since the Korean war ended in an uneasy truce in 1953.
State media anointed Kim's youngest son, Kim Jung-un, as the "Great Successor," but little is known about how he would run a reclusive state with more than a million troops and missiles that Washington fears could one day reach U.S. shores.
Many experts have warned that a transition could lead to a period of instability. In a reminder of the permanent volatility on the divided peninsula, South Korean media reported that the North test fired a short-range missile off its eastern coast.
The North's biggest ally, China, expressed official grief over Kim's sudden death and, in an important signal, threw its weight behind his apparent successor, Kim Jung-un.
President Barack Obama and South Korean and Japanese leaders spoke by telephone to discuss the situation, which was unfolding well into Washington's night.
South Korea, still technically at war with the North, put its military on alert after the news of the death, Yonhap news agency said, and President Lee Myung-bak convened its National Security Council. Seoul's Defence Ministry said there were no signs of any unusual North Korean troop movements.
The White House released a short statement committing itself to working with both South Korea and Japan, two of its closest Asian allies, to ensure continued stability in the region.
"We remain committed to stability on the Korean peninsula, and to the freedom and security of our allies," White House press secretary Jay Carney said in a short written statement.
European countries spoke of the opportunity for change.
"This could be a turning point for North Korea. We hope that their new leadership will recognize that engagement with the international community offers the best prospect of improving the lives of ordinary North Korean people," British Foreign Secretary William Hague said in a statement.
German Foreign Minister Guido Westerwelle said: "We call on the new leadership in North Korea to use the change of leadership for reform. The people are suffering under this dictatorship. They need new chances for prosperity and a new impetus for the peace process."
"PREPARE FOR THE UNEXPECTED"
Japan convened a special security meeting, although it stopped short of putting its armed forces on special alert.
"Prime Minister (Yoshihiko) Noda instructed ministers at the security meeting to prepare for the unexpected, including financial matters, North Korea's domestic issues and border affairs," Japan's top government spokesman said on Monday.
Noda told reporters it was important that Kim's death did not adversely affect peace on the Korean peninsula. He also said there was no change in Japan's demand for the return of Japanese citizens abducted by North Korean agents decades ago.
Many experts believe the Kim dynasty would collapse without support from its main ally China. There was initially a yawning four-hour silence from Beijing before it praised Kim Jong-il.
"We feel incomparably anguished, and offer our deepest condolences to the entire North Korean people," China's top leaders said in a statement read out on state TV, which called Kim a "great leader."
"We are sure that the North Korean people will abide by Comrade Kim Jong-il's will and unify around the Korean Workers' Party, and under the leadership of Comrade Kim Jung-un turn their anguish into strength."
President Dmitry Medvedev sent condolences from Russia, North Korea's other giant neighbor and friend. Foreign Minister Sergei Lavrov told reporters: "Of course, we hope that the loss which has befallen this amicable people will not affect the future development of our friendly relations."
China, Russia, the United States, Japan, South Korea and North Korea make up the so-called "six-party talks," a troubled dialogue aimed at persuading Pyongyang to scrap nuclear programs and give up ambitions to develop nuclear weapons.
The talks collapsed in 2008, though there have been some fruitless diplomatic efforts since then to revive them.
EU foreign policy chief Catherine Ashton said the European Union was monitoring the situation.
Australia, which fought for the South in the Korean war and maintains diplomatic relations with Pyongyang, called for calm, especially around the demilitarized zone separating the Koreas.
"It's at times like this that we cannot afford to have any wrong or ambiguous signaling," said Foreign Minister Kevin Rudd, who visited the heavily fortified border zone last month.
"This is the single largest militarily armed zone anywhere in the world and we need to ensure that calm and restraint are exercised in an exceptionally difficult period of transition."
Taiwan set up an emergency committee within its Foreign Ministry to monitor developments on the Korean peninsula.
(Reporting by Reuters bureaux; Writing by Mark Bendeich and Peter Graff; Editing by Matthew Jones)