Tearful reaction to Kim's death
00:47 - Source: CNN

Story highlights

NEW: "An insecure North Korea could (be) more dangerous," a U.S. official says

NEW: South Korea's national security council is convening, its president says

Kim died of a heart attack while on a train, North Korea's state news agency reports

Kim Jong Il was the son of Kim Il Song, the founder of the communist nation

CNN  — 

North Korea’s enigmatic leader Kim Jong Il – who, after succeeding his father 17 years ago, captained his poor, closed nation and antagonized its enemies – is dead, state media reported Monday.

Kim, 69, died at 8:30 a.m. Saturday, according to state media.

A tearful broadcaster reported that Kim died due to “overwork” after “dedicating his life to the people.”

Kim suffered “great mental and physical strain” while on a train during a “field guidance tour,” North Korea’s state-run KCNA news agency reported.

A look back at the life of Kim Jong Il

More specifically, the agency reported that Kim suffered a heart attack and couldn’t be saved despite the use of “every possible first-aid measure.”

He had been treated for “cardiac and cerebrovascular diseases for a long period,” KCNA noted.

His funeral will be held December 28 and the national mourning period extends until December 29, said the news agency.

North Korean and communist party officials “released a notice on Saturday informing” members of the Workers’ Party of Korea, military “and all other people” of Kim’s passing, according to KCNA.

South Korea’s national security council convened after news broke about Kim’s death and was still meeting as of 2 p.m. Monday, President Lee Myung-bak’s office said.

The president canceled the rest of his Monday schedule, and all members of South Korea’s military have been placed on “emergency alert,” according to Lee’s office.

Under the alert – which is short of the highest possible level – South Korean forces will monitor North Korean troop movements closely and tighten security measures at sea, according to the ministry of defense.

In addition, South Korea’s National Police Agency has ordered police across the country to be on emergency work shifts.

“South Korea’s concern is warranted, frankly, because an insecure North Korea could well be an even more dangerous North Korea,” a U.S. official said.

The White House, meanwhile, released a statement saying U.S. officials are “closely monitoring reports” of Kim’s death and are “in close touch with our allies in South Korea and Japan.”

This Just In: Up-to-the minute news on the death of Kim Jong Il

“We remain committed to stability on the Korean peninsula, and to the freedom and security of our allies,” the White House statement said.

The son of Kim Il Song, founder of the communist nation, Kim Jong Il had been in power since 1994 when his father died of a heart attack at age 82.

The enigmatic leader was a frequent thorn in the side of neighboring South Korea, as well as the United States. There have been reports in recent years about his health, as well as that power will be transitioned to his son, Kim Jong Un.