Governments around the world are watching warily developments in North Korea following the sudden death of Kim Jong Il.
Cautious optimism that the demise of the 69-year-old dictator could usher in a new era of change was tempered by uncertainty as to how the notoriously unpredictable regime would react.
Foreign Secretary William Hague voiced the hope that the end of Kim's 17-year despotic reign could mark a "turning point" in the history of the impoverished, nuclear-armed, Stalinist state.
In contrast, South Korea, which remains technically at war with its neighbour, put its forces on a state of high alert amid fears the regime could react with a show of strength.
State media in Pyongyang signalled power would now pass to Kim's third son, Kim Jong Un, hailing him as the "great successor".
Little is known in the West about the younger Kim, who is thought to be in his late 20s and was educated in Switzerland.
Since last year he has been publicly groomed as heir apparent to his father, who suffered a stroke in 2008, and it had been thought there would have been further moves to prepare him to assume the mantle of power during 2012.
Mr Hague urged the new leadership to end the country's years of virtual isolation and engage with the rest of the world, although he admitted it was "difficult to be optimistic" that the country would change.
"This could be a turning point for North Korea," he said in a statement.
"We hope that their new leadership will recognise that engagement with the international community offers the best prospect of improving the lives of ordinary North Korean people."