As talks over Iran’s nuclear programme resume in Geneva, the US has warned it would be “very hard” to seal a breakthrough deal this week.

However cautious optimism remains that a deal can be reached.

Foreign Minister Mohamed Javad Zarif is leading Iran’s negotiating team in a meeting with envoys from Russia, the United States, China, France, Britain and Germany in the hope of reaching an initial accord.

It would mean Iran limiting its contested uranium enrichment in exchange for limited relief from sanctions.

Euronews correspondent in Geneva, Farriba Mavvadat, says behind the scenes sources say that as the position of the E3+3 (P5+1) changes regularly, Iran’s position stays put. Catherine Ashton said the negotiations were positive and Iranian Foreign Minister Zarif is optimistic about reaching an agreement.

This round of talks has been scheduled to last three days. However Catherine Ashton’s spokesperson, Michael Mann, told euronews the talks were a gradual process and would take time.

“It is always been the approach that there would be a first step, a confidence building step, and then there would be follow up steps. This is so complicated, that is not something you can simply deal with overnight. We are working in the way we’ve always been working to get an understanding with the Iranians that is robust, that is sustainable, that is verifiable, but of course there would need follow up work even if we reached an initial agreement.

“The dynamic for the next couple of days is yet to be decided. We will decide on the basis of what happened so far, how we will organise the work, but we just want to drive things forward, we want to have further narrowing of positions and make as much progress as we can. The most important thing is that any agreement that is done is a good deal, so it will take as long as it takes.”