The United States and the United Nations have urged restraint following naval actions by North Korea and South Korea in the Yellow Sea. An Obama administration spokesman spoke Tuesday. He said the United States hopes North Korea will not take future actions that could be seen as aggressive. A U.N. official says Secretary General Ban Ki-moon is carefully observing the situation. South Korea says one of its naval ships fired warning shots at a North Korean boat that entered its territorial waters. South Korea says the boat suffered heavy damage before it withdrew. North Korea's official news agency says its boat was on an operation to confirm an unidentified object on its side of the border.