of some air defense radars that might be able to detect incoming aircraft. deployment of additional artillery pieces near the dmz. the concern, north korean artillery could hit population centers such as seoul in the south. signs of a potential preparation for a scud missile launch and dozens of warships and submarines headed out to sea. >> now it's up to the north to act and not simply just make assurances with respect to their own military activities there along the border. >> reporter: u.s. officials tell cnn they had two major worries. first, the north koreans took the unusual step of giving a specific deadline for threatening to attack the south if it did not stop loud speaker propaganda broadcasts. and second that the south korean government was considering military retaliation in addition to artillery shells