North Korea has threatened to continue launching strikes against South Korea if it violates their disputed sea border.
The warning followed its bombardment of a South Korean island near the western border.
South Korean officials said the barrage set buildings on fire and killed at least two marines after North Korea warned the south to halt military drills in the area.
North Korea’s supreme military command said if the border was violated “even 0.001 millimetre” that it would “launch merciless military retaliatory strikes.”
South Korea said it had returned fire and scrambled fighter jets in response to the attack from the north, and said bombardment of civilian areas violated the 1953 armistice halting the Korean War. The two sides technically remain at war because a peace treaty was never negotiated.
The skirmish came amid high tension over North Korea’s claim that it has a new uranium enrichment facility and just six weeks after North Korean leader Kim Jong Il unveiled his youngest son Kim Jong Un as his heir apparent.
The United States, which has tens of thousands of troops stationed in South Korea, condemned the attack and called on North Korea to “halt its belligerent action.”
British Foreign Secretary William Hague urged Pyongyang to refrain from further attacks, which he described as “unprovoked”.
The North’s artillery struck the small South Korean-held island of Yeonpyeong, which houses military installations and a small civilian population and which has been the focus of two previous deadly battles between the Koreas.
The firing came amid South Korean military drills in the area. North Korea’s military had sent a message to South Korea’s armed forces earlier to demand that the drills stop, but the South continued them, a military official said.