The United States and South Korea have agreed to "coordinate" any response to North Korea after Pyongyang's deadly artillery attack on a South Korean island provoked global condemnation. The assault Tuesday which killed two South Korean marines was one of the most serious border incidents since the 1950-1953 war. South Korea's military went on top alert, its troops fired back with cannon and the government met in an underground war room, officials said, in response to what Seoul called an atrocity against civilians. North Korea's supreme command, however, accused South Korea of firing first and vowed "merciless military attacks with...