US and South Korean troops began major war games aimed at deterring North Korea's military threat amid tension over the communist state's nuclear capability.
The annual exercises, called RSOI/FE 03, will be staged throughout South Korea until April 2nd. They will be backed by a US aircraft carrier positioned near the Korean peninsula.
Thousands of US soldiers have already been out near the heavily armed inter-Korean border for a warm-up mock battle ahead of RSOI/FE 03.
Seoul and Washington have refused to reveal the number of soldiers in the exercises, which they said are designed to improve the ability of allied forces to defend South Korea against an invasion by North Korea.
Last year, the exercises involved hundreds of thousands of South Korean and US troops.
North Korea has condemned the joint drills as preparations for an invasion.