North Korea's new leader vowed in 2009 to wage war if the country's enemies shot down its long-range rocket, state TV footage showed in the first official word of his role in military operations before his father's death. Meanwhile, South Korean President Lee Myung-bak is on his way to Beijing today to meet with Chinese President Hu Jintao.
The documentary aired on Sunday is the second in a week seeking to highlight Kim Jong Un's experience in leading North Korea's 1.2 million-strong military and was aimed at showing that he was in charge of the armed forces long before his father, former leader Kim Jong Il, died of a heart attack last month.
The son, who is in his late 20s, has moved swiftly into the role of "supreme leader" of the people, the ruling Workers' Party and the military despite questions abroad about how easily he could assume power with only a few years of grooming behind him. Kim Jong Il, in contrast, had 20 years of training when his father, North Korea founder Kim Il Sung, died of a heart attack in 1994.
Where a North Korea under Kim Jong Un is headed is deemed crucial because the country is locked in a long-running stand-off over its nuclear ambitions and is grappling with chronic food shortages. North Korea has tested two atomic devices and is believed to be working towards mounting a bomb on a missile capable of reaching the US
After years of acrimony, Pyongyang and Washington had begun discussions about food aid and how to restart nuclear disarmament talks that were suspended when Kim died last month. The US and North Korea fought on opposite sides of the 1950-53 Korean War and do not have formal diplomatic relations.
South Korean President Lee Myung-bak is on his way to Beijing today to meet with Chinese President Hu Jintao.
Mr Lee will "discuss ways to develop the strategic partnership between the two nations and cooperative measures for peace and stability on the Korean peninsula", according to a press statement.
Mr Lee will be in China for three days.
This is the first major meeting between the two since North Korean leader Kim Jong-il's death.
Mr Lee is also expected to meet with top Chinese legislator Wu Bangguo before meeting with Mr Hu, officials said.
Observers say Seoul wants closer co-ordination with Beijing on the issue of North Korea.
China, North Korea's main ally and key trade partner, was quick to endorse Kim Jong-un's leadership after his father's death on 17 December.
It is also the chair of the stalled six-party talks aimed at persuading North Korea to end its nuclear ambitions.