The death of North Korean leader Kim Jong-il could dim hopes for fresh nuclear disarmament talks with the United States and its key Asian allies as an untested and largely unknown heir takes charge of one of the world's most feared atomic renegade states.
The most crucial immediate question for Washington, and close ally Seoul, is whether Kim's hermetic state can survive his death and complete a power transition to his youngest son Kim Jong-un, named by state news agency KCNA as the Great Successor to his father.
The reason people are watching closely is not because we expect the North to strike out, it's because events within North Korea could have unsettling ramifications, said Rod Lyon, a Korea expert at the Australian Strategic Policy Institute in Canberra.
If there's a contested succession, it means there's a struggle over things like who controls North Korea's plutonium, not just who controls North Korea's army.
The White House said President Barack Obama was in close touch with South Korea and Japan, two of the other countries engaged in six-nation talks on North Korea's nuclear program.
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 written statement.
The other key regional player is China, the closest North Korea has to a major ally and which has a sometimes testy relationship with the United States.
China's biggest worry will be over North Korea's stability, and China's aim will be to ensure the country remains stable, said Cai Jian, a Korea expert at Shanghai's Fudan University.
I think security will be stepped up in North Korea, and China is also likely to tighten security along the border. If (Kim's) death leads to chaos, we could see a flow of refugees across the (Chinese) border.
TRICKY TIME FOR OBAMA
For Obama, Kim's death comes at a tricky time as the administration weighs whether to re-engage with Pyongyang on the nuclear issue and whether to provide food aid for millions of North Koreans hard hit by shortages.
The U.S. envoy for North Korean nuclear issues, Glyn Davies, has just returned to Washington for consultations after talks in Seoul, Tokyo and Beijing over the nuclear issue.
U.S. officials have said no decision is imminent on restarting negotiations on Pyongyang's nuclear program, but they have recently relaunched talks with North Korean diplomats on resuming food aid - a step widely seen as a positive signal.
The United States and its main Asian allies have resisted calls to restart the so-called six-party talks involving the two Koreas, the United States, China, Japan and Russia which broke down in 2008. United Nations inspectors were expelled from North Korea in 2009.
Some analysts said Kim's death and the transition to a young and untried leader - little is known about Kim Jong-un, who is believed to be still in his late 20s - could darken the outlook for the nuclear talks.
Everyone's immediate refrain is 'Oh, great, a tyrant is gone,' said Jim Walsh, North Korea expert at the Massachusetts Institute of Technology's security studies program.
But actually this is bad news, because it means we are entering a more dangerous phase in North Korean, South Korean and U.S. relations. Naturally, North Korea is going to be on the offensive. This young leader is going to have to prove his worth.
The United States, backed by Japan and South Korea, has demanded North Korea signal its sincerity on nuclear talks by halting provocative actions such as last year's sinking of a South Korean warship and shelling of a South Korean island.
Some North Korea watchers have attributed the two attacks to efforts by the younger Kim to demonstrate his leadership style, leading to fears that new provocations could strain the already tense relationship between North and South Korea.
Kim Jong-un ... may feel it necessary in the future to precipitate a crisis to prove his mettle to other senior leaders or to generate a 'rally-around-the-flag' effect, said Bruce Klingner, Asia policy analyst at the Heritage Foundation in Washington, adding he believed fresh North Korean military action was unlikely in the near term.
It is likely that such negotiations (on resuming the six-party talks) would be postponed as North Korea goes through a mourning period, formalized succession process and possible retrenchment of its foreign policies, he said in a written statement.
Some North Korea experts said the leadership in Pyongyang was likely to focus internally over the medium term as it seeks to firm up control both during and after the succession.
The post-Kim Jong-il era has begun and this era will certainly bring change to the Korean peninsula, said Professor Zhu Feng, an East Asian regional security specialist at Peking University.
So, in these circumstances, regional cooperation between China and the United States, as well as Japan, South Korea and Russia, will become all the more important.
(Additional reporting by Phil Stewart and Paul Eckert in AWSHINGTON, Mary Slosson in LOS ANGELES and Alex Richardson in SINGAPORE; Editing by Philip Barbara and Ian Geoghegan)