North Korea's leader Kim Jong-Un commended an army unit involved in a deadly skirmish with the South in 2010 and ordered immediate counter-attacks if provoked again, Pyongyang's state media said.
The move comes as South Korea and the United States prepare to engage in an annual military exercise this week, described by the North as "an all-out war rehearsal" that could ignite conflict on the Korean Peninsula.
Kim praised the unit, based on Mu Islet near the disputed Yellow Sea, for its bloody exchange of shells with the South's forces on the neighbouring Yeonpyeong island in November 2010, which left four South Koreans dead.
The North's leader told the soldiers to "deal an annihilating blow immediately... if a single shell lands on the waters or land where the sovereignty of the DPRK (North Korea) is exercised", the Korean Central News Agency reported on Saturday.
He also conferred the title of "hero" on an artillery piece and "heroic defence detachment" to the army unit.
South Korea and the United States describe their annual exercises, which takes place this year August 20-31, as defensive and routine but the North terms them as a rehearsal for invasion and launches its own counter-exercises.
Tensions on the Korean peninsula rose to a new high when the South accused the North of torpedoing one of its warships with the loss of 46 lives in March 2010 near the disputed sea border.
The North denied the charge but went on to shell Yeonpyeong island near the area in November 2010.
It also attempted but failed to put a satellite into orbit in April. The United States and its allies say it was a ballistic missile test in disguise.
Pyongyang has also threatened attacks on the South's government and conservative media for perceived insults to its regime.