Iran, six world powers clinch breakthrough nuclear deal --- (Reuters) - Iran and six world powers reached a breakthrough agreement early on Sunday to curb Tehran's atomic ambitions in exchange for limited sanctions relief, in a first step towards resolving a dangerous decade-old standoff. --- The deal between the Islamic state and the United States, France, Germany, Britain, China and Russia was nailed down after more than four days of negotiations. --- "We have reached an agreement," Iranian Foreign Minister Mohammad Javad Zarif announced on his Twitter feed. French Foreign Minister Laurent Fabius also confirmed the deal. - More