South Korea’s Joint Chiefs of Staff said in a statement that it found shells that appeared to have been fired from North Korea from multiple launch rocket systems. She stated that “shots were found last night,” noting that “the army has stepped up surveillance procedures and increased alert levels,” without mentioning any other measures.

North Korea frequently tests multi-barrel rocket launchers during military exercises and has developed larger types in recent years. These smaller rockets are considered Pyongyang’s main weapon in bombing targets in South Korea in case of conflict.

North Korea has tested a number of missiles this year, all of which are banned by UN Security Council resolutions that have sanctioned Pyongyang’s missile development.

South Korea is seeking a $2.6 billion missile defense system designed to defend against North Korea’s arsenal of projectiles and long-range missiles.