North Korea fired around 130 artillery shells into the sea off its east and west coasts on Monday, South Korea's military said, in the latest apparent military drill near their shared border.
Some of the shells landed in a buffer zone near the sea border in what Seoul said was a violation of a 2018 inter-Korean agreement designed to reduce tensions.
The South Korean military sent several warning communications to the North over the firing, the ministry of defence said in a statement.
North Korea did not immediately report on the artillery fire, but it has been carrying out an increasing number of military activities, including missile launches and drills by warplanes and artillery units.
South Korea and the United States have also stepped up military drills this year, saying they are necessary to deter the nuclear-armed North.
The 2018 Comprehensive Military Agreement (CMA) was the most substantive deal to come from the months of meetings between leader Kim Jong Un and then-South Korean President Moon Jae-in.
With those talks long stalled, however, recent drills and shows of force along the fortified border between the Koreas have cast doubts on the future of the measures. South Korea has accused the North of repeatedly violating the agreement with artillery drills this year.
This year North Korea resumed testing of its long-range intercontinental ballistic missiles (ICBMs) for the first time since 2017, and South Korea and the United States say it has made preparations to resume nuclear testing as well.