North Korea's new leader Kim Jong-Un has overseen an attack drill and ordered the military to "mercilessly wipe out" their enemies in case of war, Pyongyang's official news agency said Thursday.

The agency in a report dated Wednesday did not say when or where Kim launched the "combined strike drill" by the army, navy and air force, which comes amid high tension with South Korea.

Many of the country's top military and civilian officials attended the exercise, which featured a simulated attack by planes, ships and artillery on enemy warships.

Kim was officially appointed supreme commander of the 1.2 million-member military after taking over the national leadership following the death of his father Kim Jong-Il on December 17.

His regime has agreed a surprise nuclear deal with the United States but has taken a consistently hostile tone with the South's conservative government.

It has several times threatened a "sacred" war against the South over perceived insults to the North's ruling dynasty, and Kim has toured a series of frontline military units.

Kim accused the North's enemies of awaiting a chance to make a surprise attack, the news agency said. He ordered troops "to mercilessly wipe out the enemies with arms of justice and revenge once they go into action".

South Korean troops are also planning a major military exercise. It will be held near the disputed Yellow Sea border late this month to mark the second anniversary of the sinking of one of Seoul's warships.

The South accused its neighbour of torpedoing the corvette on March 26, 2010, with the loss of 46 lives. The North denied responsibility but shelled a South Korean border island eight months later, killing four people.

South Korean and US troops are already conducting a separate annual field exercise known as "Foal Eagle". The North says such drills are rehearsals for invasion.

The South has ordered troops to stay vigilant before dozens of national leaders including US President Barack Obama gather for a Nuclear Security Summit in Seoul on March 26-27.