South Korea's military said Monday it detected about 130 artillery shells fired off North Korea's east and west coasts in violation of a 2018 inter-Korean agreement designed to reduce border tensions.

The Joint Chiefs of Staff said the shots were fired from about 2:59 p.m. from the North's Kangwon Province and South Hwanghae Province areas toward the Sea of Japan and the Yellow Sea, respectively, all of which fell into the maritime buffer zone between the two Koreas.

"Our military communicated warnings regarding 'violation of 9. 19 military agreement and instant cessation of provocation' in response to North Korea's artillery shots off the east and west coasts," the JCS said while urging Pyongyang to stop such firing immediately.

North Korea said Monday it fired more than 130 rounds as dozens of projectiles thought to be multiple rocket launcher shells were launched by South Korea, according to the official Korean Central News Agency.

An unnamed spokesman for the General Staff of the Korean People's Army said in a statement the South fired the projectiles toward the southeast direction from Gangwon Province and the North's military launched the shells as a "tit for tat" warning, according to KCNA.

"The KPA General Staff makes it clear once again that it will settle accounts with all provocative actions of the enemy one by one and will always counter them with staunch and overwhelming military action," the statement said.

The North Korean action came after South Korea, Japan, and the United States each imposed additional sanctions against individuals and institutions related to Pyongyang's development of missiles and nuclear weapons.