SEOUL — North Korea vowed Thursday to attack any South Korean ships which violate their disputed border and Seoul’s navy staged its own show of strength amid continuing high tension over the sinking of a warship.

Pyongyang’s military general staff also scrapped a pact which guards against accidental naval clashes at the flashpoint border, and repeated threats to shut down a joint business project.

Elsewhere in the Yellow Sea, South Korea’s navy staged an anti-submarine exercise, its first since Seoul publicly accused Pyongyang of torpedoing one of its warships on March 26 with the loss of 46 lives.

In Seoul, an estimated 10,000 protesters shouted “Kill our enemy!” and whacked images of the North’s leader Kim Jong-Il with wooden bars.