In their sharpest power dispute yet, Palestinian President Mahmoud Abbas on Friday blocked Hamas’ plans to set up a shadow security force, which was to be made up of militants and to be headed by the No. 2 on Israel’s wanted list. Abbas issued a presidential decree vetoing the decisions made a day earlier by Interior Minister Said Siyam of Hamas. As president, Abbas wields considerable power and has the right to approve or reject key appointments. Full Story