Iran nuke talks to continue in new phase: Officials

Lausanne: Wrapping up six days of marathon nuclear talks with mixed results, Iran and six world powers prepared on Tuesday to issue a general statement agreeing to continue talks in a new phase aimed at reaching a final agreement by the end of June to control Iran's nuclear ambitions, officials said.

Officials had set a deadline of March 31 for a framework agreement, and later softened that wording to a framework understanding, between Iran and the so-called P5+1 nations, the United States, Britain, France, Germany, Russia and China.

And after intense negotiations, obstacles remained on uranium enrichment, where stockpiles of enriched uranium should be stored, limits on Iran's nuclear research and development and the timing and scope of sanctions relief among other issues.

The joint statement is to be accompanied by additional documents that outline more detailed understandings, allowing the sides to claim enough progress has been made thus far to merit a new round, the officials said. Iran has not yet signed off on the documents, one official said, meaning any understanding remains unclear.

The talks have already been extended twice as part of more than a decade of diplomatic attempts to curb Tehran's nuclear advance.

The next stage will be presented as a new phase, because most of the parties had ruled out another prolongation of this round.

The officials spoke on condition of anonymity because they were not authorised to comment on the talks on the record.

If the parties agree only to a broad framework that leaves key details unresolved, President Barack Obama could face stiff opposition from members of Congress who want to move forward with new Iran sanctions legislation.

Lawmakers had agreed to hold off on such a measure through March while the parties negotiated.

Obama has warned that passing new sanctions during the talks could upend the sensitive discussions.

The softening of the language from a framework "agreement" to a framework "understanding" appeared due in part to opposition to a two-stage agreement from Iran's supreme leader, Ayatollah Ali Khamenei.

Earlier this year, he demanded only one deal that nails down specifics and does not permit the other side to "make things difficult" by giving it wiggle room on interpretations. Russian Foreign Minister Sergey Lavrov, who left Lausanne Monday, arrived back to the Swiss city by late afternoon, another indication that an end to the talks was near.

In Moscow, he told reporters: "Prospects for this round of negotiations were not bad, and I would even say good."

Some of the P5+1's foreign ministers joined Kerry and Iranian Foreign Minister Mohammad Javad Zarif at the talks over the weekend in an intense effort to reach a political understanding on terms that would curb Iran's nuclear activities in exchange for sanctions relief.