SEOUL, South Korea — North Korea threatened on Sunday to carry out a “new form” of nuclear test, a year after its third nuclear test raised military tensions on the divided Korean Peninsula and prompted the United Nations to tighten sanctions against the North.

The North’s Foreign Ministry did not clarify what it meant by a “new form” in its statement, carried by the North’s official Korean Central News Agency. But Washington and its allies have long suspected the country of trying to make nuclear devices small and sophisticated enough to be delivered by intercontinental ballistic missiles it was also developing.

Responding to the North’s announcement, Cho Tai-young, the spokesman for the South Korean Foreign Ministry, said in a statement that “North Korea should bear in mind that if it ignores the stern demand from the neighboring countries and the international community and carries out a nuclear test, it will have to pay a price for it.”

North Korea later told South Korea that it will carry out live-fire military drills on Monday near the rivals’ disputed western sea border, the scene of naval skirmishes in recent years. It designated seven zones for its drills and warned South Korean fishing boats out of the areas, the Office of the Joint Chiefs of Staff of the South Korean military said.