Iran and six world powers have kicked off a new round of nuclear talks in Vienna.
During their May 14-16 meeting, the sides plan to start drafting the text of a permanent agreement on Tehran's atomic activities.
The P5+1 -- the United States, China, Russia, Britain, France, and Germany -- want Iran to agree to reduce its nuclear work in exchange for lifting economic sanctions.
Under an interim deal struck in Geneva, Iran froze certain activities for six months in return for minor sanctions relief. This deal expires on July 20.
After three months of discussions, diplomats say substantial differences remain.
Michael Mann, spokesman for EU foreign policy chief Catherine Ashton, described the talks to RFE/RL as "very difficult." He said both sides are determined to reach an agreement but said "that does not mean they will reach an agrement by a certain date just for the sake of reaching an ageement by a certain date."
During a visit to Saudi Arabia on May 14, U.S. Defense Secretary Chuck Hagel promised U.S. allies in the Persian Gulf that the negotiations "will under no circumstances trade away regional security for concessions on Iran's nuclear program."
Based on reporting by AFP, Reuters, AP, and RFE/RL's Radio Farda