SEOUL, South Korea — North Korea said on Tuesday that it would cut off a hot line with the United States military in South Korea, calling the truce that stopped the Korean War in 1953 null and void and threatening to strike the United States with “lighter and smaller nukes.”

North Korea had many times said it was nullifying the Korean War Armistice that stopped, but did not officially end, the three-year war. When it wanted to raise tensions in the past, it had also cut off, and later restored, the military hot line that the American-led United Nations Command maintained with North Korea through the truce village of Panmunjom north of the South Korean capital, Seoul, to help avoid armed conflicts on the divided peninsula.

North Korea’s latest threats came as the United Nations Security Council was about to consider a new sanctions resolution, and five days after the United States and South Korea began their annual joint military exercises. North Korea has always denounced such drills as rehearsals for invasion, and its military started its own drills, with its leader Kim Jong-un visiting military units and its government exhorting the North Koreans to stay on a war footing.

“As we have already declared, we will take second and third countermeasures of greater intensity against the reckless hostilities of the United States and all the other enemies,” the supreme command of the North’s Korean People’s Army said in a statement carried by the country’s state-run Korean Central News Agency. “They had better heed our warning.”