LAUSANNE, Switzerland — Wrapping up six days of marathon nuclear talks with mixed results, Iran and six world powers prepared Tuesday to issue a general statement agreeing to continue negotiations in a new phase aimed at reaching a comprehensive accord by the end of June, officials told The Associated Press on Tuesday. The joint statement is to be accompanied by additional documents that outline more detailed understandings, allowing the sides to claim enough progress has been made thus far to merit a new round, the officials said. The talks have already been extended twice as part of more than a decade of diplomatic attempts to curb Tehran’s nuclear advance, and the next stage will be presented as a new phase, because most of the parties had ruled out another prolongation of this round. One of the officials said the statement was general in part because differences between the sides remained ahead of a new phase of negotiations toward a comprehensive deal by late June.