U.S. officials are increasingly concerned that North Korea may be preparing its first test of a nuclear weapon, though they warn that the information is sketchy and not definitive. A top U.S. diplomat, Assistant Secretary of State Christopher R. Hill, flew to the region yesterday to consult over the weekend with officials in Beijing, Tokyo and Seoul about the signs that a test may be in the works. Officials especially want China, North Korea’s main patron, to use its leverage with Pyongyang to stop it from conducting a test. Full Story