The message was sent over the radio in English , reports say . Such threat happen routinely before U.S.-South Korean exercises . The threats come in the wake of a recent nuclear test in North Korea . Key Resolve will involve 10,000 South Korean troops and 3,500 U.S. troops in exercises March 11 to 21 . North Korea 's military is already in a state of high readiness .
The message was sent over the radio in English , reports say . Such threat happen routinely before U.S.-South Korean exercises . The threats come in the wake of a recent nuclear test in North Korea . North Korea 's military is already in a state of high readiness .