VIENNA (AP) — A once-promising U.N. attempt to probe suspicions that Tehran worked on atomic arms is faltering — and with it, hopes that Iran and six world powers can meet their July target date for an overarching nuclear deal.

With efforts to draft the text of an agreement starting in Vienna on Wednesday, both sides say that meeting the informal July 20 deadline remains possible. The U.S. administration gives it a 50-50 chance, and Iranian Foreign minister Mohammad Javad Zarif recently said the talks are progressing at an “unexpectedly fast pace.”