Pyongyang - Kim Jong-il, the top leader of the Democratic People's Republic of Korea (DPRK), passed away on Saturday at the age of 69 "from a great mental and physical strain", the country's official KCNA news agency reported on Monday.
Kim died "from a great mental and physical strain at 08:30 (2330 GMT Friday) Dec 17, 2011, on a train during a field guidance tour", said the report.
Kim, who had received medical treatment for his cardiac and cerebro-vascular diseases for a long period, suffered "an advanced acute myocardial infarction, complicated with a serious heart shock" on the train, it added.
The report said every possible first-aid measure was taken immediately, which failed to save Kim's life, adding that an autopsy on Sunday "fully confirmed the diagnosis of his diseases".
In Seoul, South Korea was put on high alert on Monday, following Kim's death.
Immediately after the KCNA reported Kim's death, South Korean President Lee Myung-bak convened the National Security Council (NSC) to discuss follow-up measures with cabinet ministers.
Lee reportedly ordered all government employees be put on emergency alert. South Korea's Joint Chiefs of Staff (JCS), meanwhile, put the military on emergency alert and called an emergency meeting.
The JCS has stepped up border surveillance, but no unusual activity has been detected yet, according to South Korea's Yonhap News Agency.
JCS officials are reportedly considering raising both defence readiness status and surveillance status. South Korean police also intensified vigilance.
In Washington, the White House said late on Sunday that the United States was in close touch with South Korea and Japan over the death of Kim Jong-il and remained committed to stability on the Korean Peninsula.
"We are closely monitoring reports that Kim Jong-il is dead," White House spokesman Jay Carney said in a statement.
"The president has been notified, and we are in close touch with our allies in South Korea and Japan. We remain committed to stability on the Korean peninsula, and to the freedom and security of our allies."
