Large-scale military exercises involving American and South Korean troops have begun, prompting North Korea to threaten "all-out war".
The training drills are held every year and commanders insist they are purely defensive.
But talks between North and South Korea aimed at easing tensions between the two countries broke down recently.
Three months ago the North shelled a South Korean island, killing four people.
The exercises on land, sea and in the air involve 200,000 South Korean troops and nearly 13,000 Americans - most of whom are not based in the country.
http://www.bbc.co.uk/news/world-asia-pacific-12593727
Note: 28 February 2011 Last updated at 05:33 GMT