North Korea's shelling of an island in South Korea has drawn international condemnation.
US President Barack Obama said he was "outraged" by the attack on Yeonpyeong island which set buildings ablaze and killed two marines. It was also denounced by Russia, Japan and European countries.
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 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 to demand that the drills stop, but the South continued them.
During the drills, South Korean marines on the island shot artillery toward southern waters, away from North Korea, the official said. He spoke on condition of anonymity because of military rules.
After the North's barrages, South Korea responded by firing K-9 155mm self-propelled howitzers.
The North has claimed that South Korea fired first.
President Lee Myung-bak ordered officials to "sternly respond" to North Korea's action but also called on officials to make sure that the "situation would not escalate," according to a presidential official.
In a message to North Korea's armed forces, South Korea's military urged the North to stop provocations and warned of strong measures unless the North stopped.