North Korea says it will scrap a pact aimed at preventing accidental armed clashes with South Korea amid tensions over the sinking of a South Korean warship.

In a statement broadcast by Pyongyang’s official news agency on Thursday, the North Korean military also warned of an immediate attack if the South violates the disputed maritime border in the Yellow Sea.

The statement said Pyongyang will “completely nullify” the 2004 inter-Korean accord that calls for both navies to communicate through a common radio frequency and maintain a hotline to handle emergencies.

Cutting the hotline, installed in 2004 after deadly skirmishes in 1999 and 2002, raises the chances of an armed clash in tense waters between the two neighbors.

“We will immediately deliver a physical strike at anyone intruding across our maritime demarcation line,” the news agency quoted a senior military official as saying, referring to the North’s self-proclaimed sea border.

The North said in the statement that it will also ban South Korean personnel and vehicles from entering a joint industrial park at the North Korean border town of Kaesong.

The announcement comes after South Korean warships took part in a major anti-submarine drill.

The South Korean warship the Cheonan, went down around two months ago near the disputed inter-Korean maritime border, raising tensions between the two nations, which technically remain at war.”