North Korea launched at least 10 missiles on Wednesday, South Korea’s military said, following an earlier announcement that a short-range ballistic missile had landed perilously close to the two nations’ sea border for the first time. The announcement out of Seoul was reported by the Associated Press and Agence France-Presse. South Korea’s military command called the move “unprecedented and unacceptable,” with President Yoon Suk-yeol calling an emergency meeting shortly after the launch. One of the three short-range ballistic missiles reported earlier on Wednesday by South Korea flew toward the Northern Limit Line, splashing down 16 miles from South Korean waters. It landed just over 100 miles from Ulleungdo, a South Korean island, prompting an air raid alert to go off. News programs flashed a warning to citizens to “evacuate to the nearest underground shelter,” according to the AP. Analysts told the AFP that North Korea’s action was one of the most “aggressive and threatening” in years, and comes after Pyongyang expressed outrage at the U.S. and South Korea’s recent joint military drills, labeling them a provocation.