U.S. and South Korean warships and helicopters are practicing antisubmarine maneuvers off the Korean Peninsula on July 26.
The four-day "Invincible Spirit" exercises involve 20 ships, 200 aircraft, and about 8,000 U.S. and South Korean sailors.
They are being held in response to the destruction of South Korean navy vessel Cheonan in March, which has been blamed on North Korean torpedo.
North Korea has strongly protested the exercises, saying they are a provocation and threatening retaliation. It vowed to respond with a "sacred war" and a "powerful nuclear deterrence."
The exercises are the first in a series of U.S.-South Korean maneuvers conducted in the East Sea off Korea and in the Yellow Sea closer to China's shores in international waters.
compiled from agency reports