The Joint Chiefs of Staff (JCS) says South Korean military authorities have informed North Korea that the communist nation’s firing of artillery shells over the maritime border in the Yellow Sea August ninth was a violation of a ceasefire agreement.

A JCS official said Thursday that the warning was given due to concerns of potential damage that could result from the firing of artillery shells.

The official said the North’s latest firing of shells was intended to be hostile and was deliberately aimed at the maritime border, which is a breach of the armistice that bans hostile actions.