Part-NIC-Nic6385774-1-1-0Iran and six world powers begin a final round of nuclear talks in Vienna Tuesday, six days before a deadline for a deal with differences still considerable despite months of negotiations. “We still have gaps to close and do not yet know if we will be able to do so,” a senior US official warned late Monday. If the sides do strike an accord, it would consign to history a 12-year standoff between the West and the Islamic republic over its nuclear programme by making any Iranian drive to make atomic weapons virtually impossible. More