Wall Street tumbles after N.Korea test, rate hike worry

By Chuck Mikolajczak NEW YORK (Reuters) - U.S. stocks dropped on Friday as investors were unnerved by a nuclear test by North Korea and comments by a U.S. Federal Reserve official that pointed towards an interest rate hike. North Korea conducted its fifth and biggest nuclear test on Friday and said it had mastered the ability to mount a warhead on a ballistic missile, drawing condemnation from the United States as well as China, Pyongyang's main ally. There was further pressure on the equity mar