North and South Korea exchanged warning shots in waters off the west coast of the Korean Peninsula on Monday, after South Korea’s military accused a North Korean merchant vessel of crossing a maritime boundary. The exchange of artillery fire came after South Korean forces joined the USS Ronald Reagan carrier battle group for U.S.-led war games off the Korean Peninsula. It follows a record pace of weapons tests carried out by North Korea this year. On Monday, South Korean President Yoon Suk-yeol promised a strong military response to what he said were plans by North Korea to carry out its first nuclear weapons test in more than five years.

President Yoon Suk-yeol: “Not only has it openly announced its intentions to preemptively use nuclear weapons, it appears that preparations for a seventh nuclear test have already been completed. … We will strengthen our deterrence against North Korea with overwhelming capabilities, through the combined defense posture of South Korea and the United States, as well as security cooperation between South Korea, the United States and Japan, so that our people can live their daily lives with confidence.”