After three months of broad discussions between Iran and the United States, France, Russia, Britain, China and Germany, the sides plan during their May 14-16 meeting in the Austrian capital to start drafting the text of a final accord that could put an end to years of hostility and mistrust.
Wide differences must still be overcome, especially regarding the size of Iran's uranium enrichment program, and a successful outcome is far from guaranteed.
Iran denies Western allegations that it has been seeking to develop the capability to make atomic bombs, saying its nuclear program is a peaceful energy project. REUTERS