A senior Iranian official has claimed a significant step forward at nuclear talks in Geneva, saying Tehran's proposed plan for resolving the decade-long impasse over its atomic programme has been accepted.

Abbas Araqchi, the deputy foreign minister, said the six world powers at the talks had "accepted the framework of Iran's proposal".

"The aim of both sides is to sign the agreement," he told Iranian journalists after the first session of talks.

He said further progress was expected at a scheduled meeting on Thursday evening in Geneva. "We hope we can all reach an agreement on a single text and that an agreement would be signed between two sides. We are currently working on this issue but it is too early to say if we will have a written agreement or it will be deferred to the next meeting or the next ones," Araqchi said.

It is believed the Iranian framework involves clinching an interim partial deal that would slow down or stop key elements of the progress of Iran's nuclear activity in return for limited sanctions relief. That would buy time for a more comprehensive deal, to be negotiated over the course of a year, which would set long-term limits for the Iranian programme.

"It's too early to say whether a written agreement could be made in the next 48 hours," Araqchi said, hinting that a further session might be required. But his account of progress at the talks was the most upbeat from a Iranian official in many years.

In another hopeful sign, the leader of the Iranian delegation, Mohammad Javad Zarif, the foreign minister, cancelled a trip to Rome so that he could take part in Thursday evening's face-to-face meeting with the EU foreign policy chief, Catherine Ashton, who acts as the convenor for the six-nation negotiating group that includes the US, UK, France, Germany, Russia and China.

Furthermore, the format of the talks in the afternoon were changed in an attempt to make possible more rapid progress. Araqchi said both sides agreed to hold four brief sessions in the afternoon instead of the usual long sessions. According to Araqchi, Iran will meet France, Britain and Germany in one session and Russia, China and the US in three separate afternoon sessions.

In comments before the talks, a senior US official appeared to endorse the two-step approach. "In response to a first step agreed to by Iran that halts their programme from advancing further, we are prepared to offer limited, targeted, and reversible sanctions relief," the official said.

"We are not talking about touching the core architecture of the Iranian sanctions regime in this first step in any way. And if Iran does not live up to its obligations under the initial understanding, or if we cannot get a comprehensive agreement finalised, any economic relief we will have given Iran can, in fact, be reversed."

The official added: "For the first time, Iran appears to be committed to moving this negotiation process forward quickly. One of the key shifts in the Iranian strategy we've seen with this new team is a recognition that they need to move quickly to get economic relief for their people given the political platform on which they were elected. And for the first time, we aren't seeing them use this negotiating process simply to buy time."