(Adds quote, details) PARIS, **v 20 (Reuters) - U.S. Secretary of State John Kerry will travel to Vienna later on Thursday to participate in a conference with world powers and Iran on Tehran's nuclear programme, a spokeswoman said. Iran and six powers, also meeting in the Austrian capital this week, aim to reach a diplomatic agreement by a **v. 24 deadline to end a 12-year dispute over the Islamic Republic's atomic programme. "Secretary Kerry will travel from Paris, France to Vienna, Austria, this evening to check in on the Iran nuclear negotiations. ...