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North Korea's 'Dear Leader' Kim Jong Il dead at 69

Kim Jong Il, North Korea's mercurial and enigmatic leader whose iron rule and nuclear ambitions dominated world security fears for more than a decade, has died

Kim Jong Il, North Korea's mercurial and enigmatic leader whose iron rule and nuclear ambitions dominated world security fears for more than a decade, has died of heart failure. He was 69.

In a "special broadcast" today (Monday) from the North Korean capital, state media said Kim died of a heart ailment on a train due to a "great mental and physical strain" on Dec. 17 during a "high intensity field inspection." It said an autopsy was done on Dec. 18 and "fully confirmed" the diagnosis.

A spokesperson at the Unification Ministry confirmed to NBC News that Kim died on Saturday.

In September 2010, Kim Jong Il introduced his third son, the twenty-something Kim Jong Un, as his successor, putting him in high-ranking posts.

NBC's Julie Yoo reported that South Korea put its military on alert and President Lee Myung-bak convened a national security council meeting after the news of Kim's death.