SEOUL, South Korea — North Korea launched a short-range ballistic missile toward the sea Sunday, followed hours later by another projectile, South Korea’s military said, in the latest escalation amid deteriorating relations over U.S.-led military exercises in the region. The missile traveled about 450 kilometers, or 280 miles, toward waters off North Korea’s eastern coast, according to South Korean officials. The military did not identify the second projectile, which was launched later from the same general area. South Korea said it increased surveillance and was coordinating information about the launches with the United States and Japan. Its presidential office convened an emergency national security council meeting and called on Pyongyang to stop conducting ballistic missile tests, which are prohibited under United Nations Security Council resolutions. Japan’s Defense Ministry also reported detecting what it believed was a North Korean missile. It said the weapon did not land in Japanese territorial waters but provided no additional details about its trajectory or impact location. The launches came two days after Kim Yo Jong, the sister of North Korean leader Kim Jong Un and a senior government official, said her country would take stronger steps to reinforce its nuclear deterrent. She described recent U.S.-led military activity as an effort to preserve American dominance in the Asia-Pacific region. North Korea has repeatedly condemned joint exercises involving the United States and South Korea as preparations for an invasion. Last month, U.S. President Donald Trump ordered a substantial reduction in the annual Ulchi Freedom Shield exercise, citing his relationship with Kim Jong Un and an apparent interest in reopening diplomacy. Kim Yo Jong dismissed the move, saying a shorter drill remained provocative and aggressive. North Korea later fired roughly 10 short-range ballistic missiles toward the sea, apparently carrying out a threat to respond to the U.S.-South Korean exercise. Earlier this month, it also conducted what it described as a live-fire drill involving missiles, artillery and drones, shortly after a five-day military exercise involving the United States, South Korea and Japan. The North Korean drills appear designed in part to improve its ability to overwhelm South Korean and U.S. missile defenses, according to the account of the exercises. Kim has accelerated development of the country’s nuclear weapons program since diplomacy with Trump broke down in 2019. North Korea has also strengthened ties with Russia and China, developments that analysts say could give Kim greater leverage in any future negotiations. Kim has said the country could return to talks if Washington abandons what he calls its hostile policy and accepts North Korea’s status as a nuclear-armed state.