WASHINGTON (Reuters) - U.S. Secretary of State Rex Tillerson, in remarks later on Tuesday, plans to say that he is optimistic about North Korea denuclearization talks and that there is no role for President Bashar al-Assad in Syria s future, a U.S. official said.  The secretary is very optimistic that we can achieve denuclearization through negotiation. We are in the middle of that path and that continues,  the official told reporters ahead of two planned speeches by Tillerson. 