Kim Jong-il took over the reins of North Korea in 1994 when his father and founder of the reclusive state, Kim Il-sung, died.

North Korean leader Kim Jong-il has died of a heart attack when he was on a train trip, igniting concerns over who will now control the reclusive state and its nuclear programme.

A teary television announcer, who was dressed in black, said the leader died on Saturday of physical and mental over-work

Kim Jong-un, Kim Jong-il’s youngest son, was named by North Korea’s official news agency KCNA as the “great successor” to his father, which lauded him as “the outstanding leader of our party, army and people”.

Little is known of Jong-un who is believed to be in his late 20s and was appointed to senior political and military posts in 2010.

KCNA news agency said the elder Kim died at 8:30 a.m. on Saturday after “an advanced acute myocardial infarction, complicated with a serious heart shock”. Kim had suffered a stroke in 2008 also, but had appeared to have recovered from that ailment.

The White House informed the media that President Barack Obama had been told of Kim’s death, and it was closely monitoring and in touch with South Korea and Japan.

Japanese Prime Minister Yoshihiko Noda told ministers at a special security meeting to prepare for the unexpected, including on border affairs, Japan’s top government spokesman said.

China, North Korea’s only major ally, has not commented yet.

Tension between North and South Korea

South Korea, still technically at war with North Korea, has put its troops and all government workers on emergency alert but Seoul’s Defence Ministry said there were no signs of any unusual North Korean troop movements and President Lee Myung-bak called for people to carry on with their normal lives.

Lee talked with President Barack Obama yesterday over the telephone as the United States takes responsibility of South Korea’s security.

North Korea, which tested a nuclear device in 2006 and again in May 2009, is regarded as one of the greatest security threats in the region.

The nuclear nation has repeatedly threatened to destroy the conservative government of South Korean President Lee Myung-bak, who ended a decade of free-flowing aid to the North after taking office in February 2008.

Kim was leading a poor communist state during his 17 years in power as he used up resources to develop a nuclear arms programme and missiles aimed at neighbours Japan and South Korea.

Kim took over the reins of North Korea in 1994 when his father and founder of the reclusive state, Kim Il-sung, died.