Three North Korean patrol boats temporarily violated the inter-Korean maritime border in the West Sea Monday but later returned to Northern waters after responding to warning shots from the South's navy. According to the Joint Chiefs of Staff, a South Korean Navy ship initially fired three warning shots with a 40mm gun towards the three North Korean vessels, which had continued moving southward even after receiving the South's radioed warning messages. The vessels returned to Northern waters following the shots but later crossed the maritme border again. The North's patrol boats finally retreated after the navy's patrol vessel fired four warning shots with a 76mm gun. It is the first time that the North has violated the NLL with three vessels since the 1953 ceasefire agreement between the two Koreas.