South Korean and United States held large-scale joint military exercise called Foal Eagle to test their defence readiness against the threat from North Korea.
It will continue until the end of April 2017.
The exercise comes amid heightened tension following the latest test launch of a ballistic missile by the North in February 2017.
South Korea also has signed agreement with US Lotte Group conglomerate to secure the land to station the Terminal High Altitude Area Defense (THAAD) missile defence system.
Another exercise conducted by both countries in 2016 involved about 17,000 American troops and more than 300,000 South Koreans.
South Korea- Capital: Seoul
- Code: +82
- President: Park Geun-hye
- Currency: South Korean won
- Prime minister: Hwang Kyo-ahn
