SEOUL, Nov. 18 (UPI) -- North Korea accused the United States on Tuesday of setting off a potential "nuclear domino phenomenon" in Asia by backing South Korea's push to build nuclear-powered submarines, warning the move would trigger an arms race and heighten regional instability. Washington and Seoul issued a joint fact sheet on Friday outlining a finalized trade and security deal that included U.S. approval for South Korea's long-sought plan to develop nuclear-powered submarines . In its