SEOUL—The U.S. and South Korea are readying for a new joint military exercise, the type of drill that in the past has prompted Pyongyang to respond with missile tests.

The two nations will this week start a five-day drill off the Korean Peninsula, involving more than 40 naval vessels and both countries’ air forces, according to South Korea’s navy. The USS Ronald Reagan aircraft carrier and the USS Stethem and USS Mustin destroyers will be deployed for the exercise, the commander of the U.S. Seventh Fleet said.

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