South Korean Army soldiers patrol on Unification Bridge in Paju, South Korea, near the border village of Panmunjom, Tuesday, April 16, 2013. North Korea's state media said Tuesday the Supreme Command of the Korean People's Army issued an ultimatum demanding an apology from South Korea for "hostile acts" and threatening that unspecified retaliatory actions would happen at any time. (AP Photo/Ahn Young-joon)

Photo by: Ahn Young-joon

South Korean Army soldiers patrol on Unification Bridge in Paju, South Korea, near the border village of Panmunjom, Tuesday, April 16, 2013. North Korea's state media said Tuesday the Supreme Command of the Korean People's Army issued an ultimatum demanding an apology from South Korea for "hostile acts" and threatening that unspecified retaliatory actions would happen at any time. (AP Photo/Ahn Young-joon)