FILE PHOTO: A combination photo shows North Korean leader Kim Jong Un (L) in Pyongyang, North Korea and U.S. President Donald Trump (R), in Palm Beach, Florida, U.S., respectively from Reuters files. REUTERS/KCNA handout via Reuters & Kevin Lamarque (R)

WASHINGTON (Reuters) - Singapore has emerged as the likeliest location for a planned summit meeting between U.S. President Donald Trump and North Korea leader Kim Jong Un, a U.S. official said on Wednesday.