Envoys from Iran and six world powers noted the positive negotiating atmosphere but kept expectations low as they started talks on Tuesday in Vienna on a comprehensive deal to end the stand-off over Tehran’s nuclear programme.

“We had a promising start this morning and we hope to continue this trend in the next three days,” Iranian Deputy Foreign Minister Abbas Araghchi said.

Building on an interim deal that was reached in November in Geneva, Iran and the five permanent UN Security Council members plus Germany are aiming to agree on further limits to Iran’s nuclear programme to rule out that it could build a nuclear weapon, in return for the permanent lifting of all sanctions against Tehran.

However, officials stressed this week’s round had the modest goal of agreeing on the timing and political level for the diplomatic process ahead.

“The aim is to create a workable framework to make the talks proceed as smoothly as possible,” said Michael Mann, the spokesman of EU foreign policy chief Catherine Ashton.

Iranian Foreign Minister Mohammad Javad Zarif, said that “this is the first step of the end phase; therefore, expectations must not be high.”

Both sides want to agree on a long-term timeframe during which Iran would further cut back its uranium enrichment, limit its uranium stock, remove doubts about its plutonium-producing Arak reactor project and allow even more intrusive inspections.

In return, the sextet is offering to permanently scrap all remaining sanctions, including the ban on Iranian oil exports that have added to Tehran’s economic woes.

The Geneva deal, which has been implemented since January, consists of only partial enrichment curbs and the suspension of a limited set of sanctions.

While many countries worry that Iran could use uranium or plutonium to build a nuclear weapon, Tehran’s leaders insist that they are only interested in civilian nuclear technology.

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