By late July, Western governments hope to hammer out an accord that would lay to rest their suspicions that Iran is seeking the capability to make a nuclear bomb, an aim it denies, while Tehran wants a lifting of economic sanctions.
Wide differences remain on how this could be achieved, although the two sides said on Thursday they agreed during meetings this week in the Austrian capital on an agenda and timetable for the talks on such an accord.
"We have had three very productive days during which we have identified all of the issues we need to address in reaching a comprehensive and final agreement," European Union foreign policy chief Catherine Ashton told reporters.
"There is a lot to do. It won't be easy but we have made a good start," said Ashton, who speaks on behalf of the United States, Russia, China, France, Britain and Germany.
Senior diplomats from the six nations, as well as Ashton and Iran's Foreign Minister Mohammad Javad Zarif, will meet again on March 17, also in Vienna, and have a series of further discussions ahead of the July deadline.
Tehran denies that its nuclear programme has any latent military purposes and has signalled repeatedly it would resist dismantling its nuclear installations as part of any deal.
"I can assure you that no one had, and will have, the opportunity to impose anything on Iran during the talks," Zarif told reporters after the Vienna meeting.
A senior U.S. official who asked not to identified cautioned that their exchanges would be "difficult" but the sides were committed to reach a deal soon.
"This will be a complicated, difficult and lengthy process. We will take the time required to do it right," the official said. "We will continue to work in a deliberate and concentrated manner to see if we can get that job done."
As part of the diplomatic process, Ashton will go to Tehran for talks on March 9-10.
A diplomatic source clarified that the two sides did not produce a text of the agreed framework for future negotiations or detailed agenda for upcoming meetings, rather only agreeing a broad range of subjects to be addressed in coming months.
While modest in scope, the arrangement is an early step forward in the elusive search for a settlement that could ward off the danger of a wider war in the Middle East, reshape the regional power balance and open up big new trade opportunities with Iran, an oil-producing market of 76 million people.
For Iran, a halt to sanctions imposed by the United States, European governments and the United Nations, would end years of isolation and lift its battered economy.


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