South Korea and the United States began large annual military exercises Monday to bolster their readiness against North Korean nuclear threats after the North raised animosities with an extension of missile tests and belligerent rhetoric earlier this year, writes APNEWS.

The South Korean and U.S. forces began a computer-simulated command post training called the Freedom Shield exercise and a variety of field exercises for an 11-day run, the South Korean Defense Ministry said.

North Korea had no immediate response to the major annual drills it regards as a rehearsal for invasion. The North has staged provocative weapons tests in the past in reaction to its adversaries’ joint drills.

South Korea’s military said last week that it would conduct 48 field exercises with the U.S. forces this spring, twice the number conducted last year, and that they would involve live-firing, bombing, air assault and missile interception drills.