Both Tehran and Washington appear optimistic ahead of the deadline for reaching an agreement on limiting Iran’s nuclear programme in exchange for relief from international sanctions.

Iranian Foreign Minister Mohammad Javad Zarif and his US counterpart John Kerry have held bilateral talks in Lausanne, Switzerland, with representatives from the other “P5+1” world powers set to join negotiations to try to reach a deal by the 31 March deadline.

The deadline for negotiations has been extended twice since the original interim agreement was hammered out in Geneva in November 2013 with significant gaps remaining between the two sides’ positions.

While there are optimistic sentiments leading up to the late-March negotiations, there is also a feeling this could be the last chance to compromise before hardliners in Iran and the US will have more power to scupper future negotiations.

“In this round of talks, shared points of view emerged in some of the areas where there had been a difference of opinion, which can be a foundation for a final agreement,” Iranian President Hassan Rouhani was quoted as saying by state news agency IRNA on 21 March.

“I believe it is possible to reach an agreement and there is nothing that cannot be resolved,” he added.

On 21 March, Kerry told reporters in Lausanne that “substantial progress” had been made over the past week, but that “important gaps remain”.

“Let me once again be clear: We don’t want just any deal,” said Kerry. “If we had, we could have announced something a long time ago.”

When the last round of talks broke down in November 2014, the differences included: the number of centrifuges Tehran will be allowed to keep in its uranium enrichment programme; the level of relief from international sanctions it will receive after the initial agreement; and the duration of the deal.

Iran is negotiating for immediate relief from sanctions against its banks and energy sectors, while P5+1 group has suggested a gradual rolling back of sanctions as Tehran hits specific targets on its nuclear programme revisions.

The biggest public difference within the P5+1 appears to be between the US and France, with the latter insisting that sanctions could only be lifted if Iran explains evidence of historical nuclear warhead design.

“We have been negotiating with Iran for 12 [years]. We shouldn’t be rushed into an agreement which will have to be comprehensive,” Gerard Araud, the French ambassador to the US tweeted during the talks. “For France, any agreement to be acceptable will have to give concrete guarantees on all issues. We won’t bypass any of them.”

If Iran is given relief from sanctions, it will be hoping for significant overseas investment in its ailing oil and gas industry. Iran has announced plans to tender 17 oil and gas blocks to international oil companies (IOCs), but there is little interest while sanctions remain in place.