North Korea's new leader Kim Jong-un watched a long-range rocket launch in 2009 while being groomed to succeed his father, and threatened retaliation if the country's enemies interfered, footage released Sunday showed.

Kim Jong-un, who is believed to be in his late 20s, has been named "supreme leader" of the communist country and is consolidating his power since his father Kim Jong-il died of a heart failure on Dec. 17.

Footage aired by North Korea's Korean Central Broadcasting Station showed the young Kim and the late leader visited a launch command post on April 5, 2009, when North Korea launched a long-range rocket, carrying what it claimed was a communication satellite.

The documentary quoted the junior Kim as saying he was determined to wage war if any enemies intercepted the rocket.

The footage, which was shown on the birthday of the new leader, also showed that Kim Jong-un drove a tank and visited several military divisions. The broadcast is widely seen as a move to support his fledgling leadership.

Kim Jong-un, who inherited his father's military-first policies, was groomed to succeed his father as the next leader of the communist country since Kim Jong-il reportedly suffered a stroke in 2008.

The junior Kim made his public debut in 2010 when he was named a four-star general and vice chairman of the ruling Workers' Party.   

North Korea has vowed to build a prosperous country this year, the centennial of the birth of the late Kim Jong-il's father, the country's late founder Kim Il-sung. (Yonhap News)