The North Korean military is claiming that South Korean naval vessels trespassed into North Korean waters this week and that due to this an inter-Korean naval clash may break out.

In a statement issued by the North’s state-run Korean Central News Agency, the North’s military claimed Thursday that 16 South Korean warships trespassed near the North’s coast a dozen times on Monday.

In response, the South Korean Navy called the North’s accusation a “preposterous” claim apparently aimed at showing that the North does not recognize the Northern Limit Line maritime demarcation border drawn up by the U.S. after the Korean War.

The North’s Thursday claim was that the South Korean ships crossed a maritime line Pyongyang unilaterally introduced in 1999.