WASHINGTON, June 12 (Reuters) - The United States and Iran are not quite at the finish line, but are very close to a deal to resolve their conflict, a senior U.S. official said on Friday, adding that Washington expects to sign a deal in the coming days. "The negotiating team has got us in a very good spot, but let's see here, we're not quite at the finish line yet, but we are very close," the U.S.