Ministers convene at Iran talks but breakthrough not yet in sight

By Parisa Hafezi and Arshad Mohammed VIENNA (Reuters) - Tehran and world powers were still shy of a breakthrough at nuclear talks on Thursday as foreign ministers flew in to lend heft to negotiations that focused on how soon sanctions would be lifted and how Iran's compliance with a deal would be checked. Iran is in talks with the United States and five other big powers - Britain, China, France, Germany and Russia - on an agreement under which it would curtail its nuclear program in exchang