North Korea fired additional artillery shells into waters off its east and west coasts Friday, the South Korean military said, following its firing of a short-range ballistic missile and artillery rounds earlier in the day.

The North fired some 80 artillery shells into the East Sea from Jangjon in Kangwon Province, starting at 5 p.m., while the sound of artillery fire was heard around 200 times in areas spanning Haeju Bay and Jangsan Cape in the Yellow Sea, starting from 5:20 p.m., according to the Joint Chiefs of Staff.

The shells fell into eastern and western buffer zones north of the Northern Limit Line, the de facto inter-Korean maritime border, which were delineated under a 2018 inter-Korean agreement on reducing military tensions.

But no shells landed in South Korean waters, the JCS said.

The South Korean military communicated a warning message multiple times, through which it pointed out the North's violation of the 2018 agreement and called on the North to stop provocations, according to the JCS.

"Such continued provocations by North Korea are acts that undermine peace and stability not only on the Korean Peninsula, but also in the international community, and we gravely warn the North to immediately cease them," the JCS said in a text message sent to reporters.

It added, "Our military is tracking and monitoring related movements in close cooperation with the United States, and reinforcing a readiness posture to prepare against possible contingencies."

Early in the morning, the North flew some 10 warplanes close to the inter-Korean border, and fired an SRBM and some 170 artillery shots.

The South Korean military decried the SRBM launch and the artillery firing as a breach of U.N. Security Council sanctions and the inter-Korean military accord, respectively.