North Korea also warned that it would respond "with a powerful military strike" should its ships be stopped by international forces trying to stop the export of missiles and weapons of mass destruction.

The twin declarations, delivered by the country's state news agency, followed South Korea's announcement Tuesday that it would join the navies that will stop and inspect suspicious ships at sea. North Korea has repeatedly said that such participation would be a "declaration of war".

They followed other developments in North Korea that have added to the sense of jangled nerves across northeast Asia since Monday's underground nuclear test.

The North fired three more short-range missiles off its east coast on Tuesday, said Yonhap, the South Korean news agency. North Korea had fired two missiles into the same waters on Monday.