According to the report, North Korea fired 130 artillery shells toward the Yellow Sea and 40 more shells toward the Sea of Japan at dawn on Friday. The shells fell outside South Korea's exclusive economic zone.
The North Korean shelling violated the 2018 Comprehensive Military Agreement, which established a maritime buffer zone between Seoul and Pyongyang to reduce military tensions, South Korean President Yoon Suk-yeol said.
"We're looking into everything one by one. But it's correct that it's a violation of the Sept. 19 accord," Yoon said, as quoted by the Yonhap news agency.
The president added that Seoul was building "a readiness posture against North Korea's provocations."
Earlier in the day, North Korea launched a short-range ballistic missile toward the Sea of Japan. The missile traveled about 650 kilometers (404 miles) at a maximum altitude of 50 kilometers before falling outside Japan's exclusive economic zone, some 370 kilometers from the country's coast, Kyodo reported, citing Japanese Defense Minister Yasukazu Hamada. Hamada said that the missile flew on an irregular trajectory.
North Korea has carried out eight test launches since September 25 and over 25 since the beginning of the year. North Korea has emphasized that its test launches are being carried out in response to the refusal of the US and South Korea to stop joint military drills, which Pyongyang believes threaten regional stability.