South Korean veterans chant slogans during an anti-North Korea protest in Seoul. Photo: Reuters.

Kim Jong-il died on Saturday of a heart attack. His death has rattled the region. US leaders have been holding urgent talks with the communist state's neighbours.

Kim Jong-il, 69, had been in the process of formalising his third son, Kim Jong-un, as his successor. But the transition had not been completed and analysts fear Mr Kim's death could triggered a period of instability in the internationally isolated nuclear-armed state.

Inside North Korea, citizens appear to be mourning Mr Kim - their leader since the death of his father Kim Il-sung in 1994.

Countries around the region have been holding urgent talks about what the implications of Mr Kim's death might be.

"It is our hope that the new leadership of the DPRK (North Korea) will choose to guide their nation onto the path of peace by honouring North Korea's commitments, improving relations with its neighbours, and respecting the rights of its people," Mrs Clinton said in a statement.

"The United States stands ready to help the North Korean people and urges the new leadership to work with the international community to usher in a new era of peace, prosperity and lasting security on the Korean peninsula."

US President Barack Obama has spoken to both the South Korean and Japanese leaders to discuss the situation.

Japan's top government spokesman said Japan, South Korea and the US were considering holding high-level talks on the situation "at the soonest possible opportunity".

President Hu Jintao has visited the North Korean embassy in Beijing to offer his condolences.