A North Korean ship crossed the inter-Korean maritime border in the Yellow Sea Wednesday but later returned to Northern waters after responding to a warning message from the South's navy.

In a statement, the Joint Chiefs of Staff said an unidentified North Korean vessel crossed the Northern Limit Line (NLL) at 4:01 p.m., Korean time, and drifted about half a kilometer southward before apparently being towed back across the NLL by another North Korean ship.

The JCS said the North Korean navy failed to respond to eight radioed warnings from the South before finally answering on the ninth attempt, identifying the ship as a Northern vessel.

The border violation comes as Southern military officials continue investigating allegations that the South's navy tried to cover up previous radio messages exchanged between the naval forces of the two Koreas.