North Korea has said it will cut off all road and railway links between the two Koreas and carry out work to fortify the inter-Korean border.

A report from the General Staff of the Korean People’s Army, carried by the state-run Korean Central News Agency, said the North will begin severing the connections and building strong defense structures Wednesday.

The statement said the North was permanently closing the border with its “principal enemy” in self-defense and to deter war.

To prevent any accidental clashes near the border, the North Korean military said it notified the U.S. military by telephone at 9:45 a.m. Wednesday.

The report said the decision was a response to joint military exercises between Seoul and Washington and the deployment of U.S. strategic assets on the Korean Peninsula.