The U.S. and South Korea have launched an annual joint military exercise, with a muted response from North Korea.
The Ulchi Freedom Guardian drill, which began Monday, is largely conducted on computers. But it involves more than 80,000 South Korean and U.S. troops.
In previous years, North Korea reacted angrily to the exercises, calling them a rehearsal for war. But so far, the official media in North Korea has been silent on the event this year.
The drills follow several North-South agreements and come at a time of decreasing tensions on the peninsula.
A spokesman for the South Korean defense ministry, Kim Min-seok, says the exercises are necessary for stability on the peninsula.
"Ulchi Freedom Guardian ... is a joint military exercise by South Korea and the United States to be prepared for possible provocation from North Korea," he said. "The Korean peninsula is under constant threat from the North and the joint exercise is indispensable to maintaining stability."
Last week, North and South Korea agreed to work toward reopening a jointly-run factory park in Kaesong. On Sunday, the two sides agreed to participate in talks on reuniting families separated during the Korean War.
South Korean army soldiers take part in a South Korea-U.S. joint military exercise at a subway station in Seoul, August 20, 2013.
People take shelter from a mock gas attack during a South Korea-U.S. joint military exercise at a subway station in Seoul, August 20, 2013.
South Korean army soldiers pass by ticket gates during a South Korea-U.S. joint military exercise at a subway station in Seoul, August 19, 2013.
Students walk past South Korean soldiers wearing gas masks during an anti-terror drill at a subway station in Seoul during joint South Korean-U.S. military drills, August 19, 2013.
South Korean army soldiers put on gas masks during South Korea-U.S. joint military exercises at a subway station in Seoul, August 19, 2013.
Protesters stage a rally against South Korea-U.S. joint military exercises in front of Yongsan U.S. Army headquarters in Seoul, August 19, 2013.