Iran nuclear checks most detailed ever - Ashton
World powers and Iran have had "their most detailed talks ever" on Iran's nuclear programme, the EU's top foreign policy official Catherine Ashton says.
The two sides have held two days of discussions in Geneva. Further talks will take place on 7 and 8 November.
Baroness Ashton and Iranian FM Mohammad Javad Zarif called the talks "substantive and forward-looking".
International negotiators were carefully considering an Iranian proposal, a joint statement said.
The discussions in Geneva brought together Iranian officials and representatives of the "P5+1" - the permanent members of the UN Security Council (Britain, China, France, Russia and the US) plus Germany - also known as the E3+3.
"The participants also agreed that E3+3 and Iranian nuclear, scientific and sanctions experts will convene before the next meeting to address differences and to develop practical steps," the statement went on.
At a news conference afterwards, Mr Zarif said he hoped the talks would lead to the "beginning of a new phase in our relations" and would help resolve "an unnecessary crisis".
He said that he expected international negotiators would need time to "digest and respond to" Iran's proposal.
Iran has previously said its proposal at the two-day summit in Geneva has the "capacity to make a breakthrough".
In previous rounds, Iran and the world powers largely talked past one another but now they appear to be getting into actual details, the BBC's James Reynolds reports from Geneva.
One official at the talks suggested that the reticence to make details of the Iranian proposal public was a positive sign - real discussions don't take place in public, our correspondent adds.
Diplomats in Geneva found an unusual source of common ground with their new Iranian counterparts: concern for the status of the Iranian foreign minister's back”
White House spokesman Jay Carney said Iran had shown a "level of seriousness and substance that we have not seen before".
Russia's response, however, was more cautious. "There is no reason to break into applause; things could have worked out better," Deputy Foreign Minister Sergei Ryabkov was quoted as saying by Interfax news agency.
UK Foreign Secretary William Hague welcomed the fact that "diplomats have for the first time begun more substantive discussions with Iran".
"Iran will need to take the necessary first steps on its programme and we are ready to take proportionate steps in return," he added.
The West suspects Tehran of seeking to build nuclear weapons, but Iran says its programme is purely for peaceful purposes.Spot checks
Earlier, Deputy Foreign Minster Abbas Araqchi said snap visits to Iranian nuclear sites could be part of a "last step" of any deal.
Previous negotiating stances
In April 2013, the P5+1 proposed that Iran should:
- Cease uranium enrichment to 20%, a threshold that could lead to weapons capability
- Ship most of stockpile of 20%-enriched uranium abroad, keeping some for Tehran research reactor
- Accept a comprehensive verification regime
- Address questions about military research activity
Iran responded by demanding P5+1 should:
- Recognise Iran's "right" to enrich uranium
- Ease all UN, US and EU sanctions
Lowering uranium enrichment levels could also be part of a final deal, Mr Araqchi told Iranian media.
The Iranian team at the talks was led by Mr Zarif, although much of the actual negotiating was said to have been delegated to Mr Araqchi.
The talks are the first since Hassan Rouhani - seen as a relative moderate - became Iran's president in August.
International negotiators want Tehran to take specific steps to prevent it from ever being able to make nuclear weapons, the BBC's James Reynolds in Geneva reports.
In return, they promise to lift some of international sanctions which have been imposed in recent years.
Key international demands include the acceptance by Iran of a comprehensive verification regime - with unannounced checks - and a reduction in Iran's level of uranium enrichment.
Iran subscribed to a fuller inspection regime under the International Atomic Energy Agency (IAEA), which was known as the additional protocol, until 2006.
Mr Zarif said the reintroduction of the additional protocol was not currently being discussed.Sanctions demands
Western nations have demanded that Iran halt the production and stockpiling of uranium enriched to 20% - a step away from achieving a nuclear weapons capability.
They also want Iran to send some of its stockpiles abroad, and shut down the Fordo production site near the city of Qom, where most of the higher-grade enrichment work is done.
Since 2006 the UN Security Council has imposed a series of sanctions - including asset freezes and travel bans - on entities and people involved in Iran's nuclear programme.
Separate US and EU sanctions have targeted Iran's energy and banking sectors, crippling its oil-based economy. Iran wants the sanctions lifted.
Mr Araqchi had earlier insisted there could be no question of Iran relinquishing its stockpiles of enriched uranium.
"We will not allow even a gram of uranium to go out of the country," he was quoted as saying by Iranian media.