President Yoon Suk-yeol vowed Monday to respond firmly and sternly to any North Korean provocation as South Korea and the United States fired missiles in response to the North's missile launches the previous day.

Yoon made the remark during a Memorial Day ceremony held at Seoul National Cemetery, a day after North Korea fired eight short-range ballistic missiles into the East Sea in its third show of force since Yook took office last month.

"Even at this moment, North Korea's nuclear and missile threats are getting sophisticated," he said, referring to Sunday's tests. "North Korea's nuclear and missile (programs) are reaching the level of threatening not only peace on the Korean Peninsula but also in Northeast Asia and the world."

Yoon said his administration will deter the nuclear and missile threats while also building a "more fundamental and practical security capability."

"Our government will respond firmly and sternly to any North Korean provocation," he said. "We will make sure there isn't a single crack in protecting the lives and property of our people." (Yonhap)