SEOUL, South Korea — North Korea on Saturday warned the top American military commander in South Korea that if the United States pressed ahead with joint military exercises with South Korea scheduled to begin next month, it could set off a war in which American forces would “meet a miserable destruction.”

The warning came as the United States and South Korean militaries planned to kick off their Key Resolve and Foal Eagle joint war games, beginning early next month. The allies regularly conduct such joint military drills, and whenever they happen, North Korea warns of war and threatens to deliver a devastating blow to American and South Korean troops.

North Korea’s harsh reaction, though not unusual, came amid heightened tensions on the Korean Peninsula after the North’s third nuclear test, on Feb. 12. Washington and its allies are pushing for more sanctions against North Korea while the North vows to take unspecified steps to retaliate against such sanctions.

“If your side ignites a war of aggression by staging the reckless joint military exercises Key Resolve and Foal Eagle again under the cover of ‘defensive and annual ones’ at this dangerous time, from that moment your fate will be hung by a thread with every hour,” Pak Rim-su, chief delegate of the North Korean military mission to the inter-Korean truce village of Panmunjom, said Saturday in a message to Gen. James D. Thurman, the American commander in South Korea.