主题：朝鲜韩国互相炮击，东北亚风云再起 -- 黄河清

South Korea says it has returned fire after North Korea fired dozens of artillery shells at one of its border islands, killing two marines.

The South's military was placed on its highest non-wartime alert after the shells landed on Yeonpyeong island.

Pyongyang accused the South of firing first. The Southern military said it had conducted exercises but shelling was directed away from the North.

This is one of the worst clashes since the Korean War ended, analysts say.