SEOUL (Reuters) - North Korea stepped up its bellicose rhetoric on Tuesday, threatening to go beyond carrying out a promised third nuclear test in response to what it believes are "hostile" sanctions imposed after a December rocket launch.Pyongyang frequently employs fiery rhetoric aimed at South Korea and the United States and in 2010 was blamed for sinking a South Korean naval vessel. It also shelled a South Korean island in the same year, killing civilians.It did not spell out the actions it would take. North Korea is not capable of staging a military strike on the United States, although South Korea is in range of its artillery and missiles and Japan of its missiles.