North Korea conducts fifth and largest nuclear test

By Ju-min Park and Se Young Lee SEOUL (Reuters) - North Korea conducted its fifth nuclear test on Friday, setting off a blast that was more powerful than the bomb dropped on Hiroshima, and said it had mastered the ability to mount a warhead on a ballistic missile. Its most powerful explosion to date follows a test in January that prompted the U.N. Security Council to impose tightened sanctions that increased North Korea's isolation but failed to prevent it from accelerating weapons development.