North Korea fired a series of artillery shots over the weekend, Seoul's military said days after leader Kim Jong Un pledged to use power for power to defend the country's sovereignty.
The South Korean military detected several flight trajectories that were believed to be shots from North Korean artillery, Seoul's Joint Chiefs of Staff said late Sunday.
The suspected shots were fired between 8: 07 am 2307 GMT and 11: 03 am Sunday morning, according to the JCS, stressing Seoul maintains a firm military readiness in collaboration with the United States.
Pyongyang's official Korean Central News Agency - which typically reports on successful weapons tests 24 hours after the fact - has not released information on Sunday's shots, nor on other recent missile launches.
The North has carried out a blitz of sanctions-busting weapons tests this year, including firing an intercontinental ballistic missile at full range for the first time since 2017.
Seoul's presidential national security office held a meeting to discuss the artillery shots late Sunday, and reaffirmed the South's position of responding calmly and sternly to Pyongyang's provocations, the office said.
The presidential office said Seoul didn't immediately release its findings on the suspected artillery fire on Sunday morning, as the shots were of a traditional type with relatively low altitude and short range.
The latest volley of fire follows warnings from both Seoul and Washington that Kim's regime is preparing to carry out its seventh nuclear test - a move that US Deputy Secretary of State Wendy Sherman said would provoke a swift and forceful response.
Kim announced last week that he plans to strengthen the country's military power during a major three-day political conference that wrapped up on Friday.
South Korean Defence Minister Lee Jong-sup said on Sunday Seoul would strengthen its defence capabilities, as well as its security cooperation with Washington and Tokyo to counter the nuclear threat from Pyongyang.