South Korean and U.S. troops took part in joint computer-simulated drills called "Key Resolve" on Friday in Seoul amid high tensions on the peninsula after North Korea's military threats.
The annual joint drills started on Monday to practice the combined and joint command-post military operations to defend South Korea.
"It is a computer-assisted war game simulation planned and operated by subject matter experts and uniquely tailored for each exercise in accordance with the training goals of the commander of the exercise unit," said U.S. Lieutenant Colonel Elton Roberts during a news briefing on Friday at the Korea Battle Simulation Centre at the Yongsan Army Garrison in Seoul.
The U.S. command in the South said more than 3,000 U.S. participants from South Korea and the United States are taking part in this year's Key Resolve exercise.
Separately, about 200,000 Korean troops and 10,000 U.S. forces are expected to be mobilised for the "Foal Eagle" exercise, under the Combined Forces Command, which runs until the end of April.
Last week, North Korea announced that Pyongyang had torn up its 1953 armistice deal with Washington, threatening military action against the U.S. and South Korea if the drills continued.
On Monday, North Korea cut off the inter-Korean communication hotline, which runs through the truce village of Panmunjom.
South Korean officials have said the North is conducting military exercises that appear to be larger in scale than in previous years.
Presented by Adam Justice