The United States said Monday no state has the existing right to enrich uranium, as Iran and the UN watchdog agreed on a "roadmap for cooperation" over its nuclear programme.
As France said world powers were still close to an agreement with Iran on its disputed nuclear drive, US Secretary of State John Kerry accused the Islamic republic of scuttling the latest efforts to end the deadlock.
Speaking in Abu Dhabi, the top US diplomat insisted a deal with Iran would protect Israel and America's Gulf allies, saying "war should be the last resort" and that no state has "existing right to enrich".
"The P5+1 was unified on Saturday when we presented our proposal to the Iranians... But Iran couldn't take it, at that particular moment they weren't able to accept," said Kerry, who took part in the talks.
On Sunday Iran's President Hassan Rouhani said his government would not abandon its nuclear rights, including uranium enrichment.
"The rights of the Iranian nation and our national interests are a red line. So are nuclear rights under the framework of international regulations, which include enrichment on Iranian soil," said Rouhani.
His remarks came a day after intensive negotiations with world powers made progress but failed to produce a long-elusive deal that would curb Iran's nuclear activities.
The so-called P5+1 group and Iran will reconvene again in Geneva on November 20 to try to iron out differences.
The broad outline of the agreement is said to include a freeze of part or all of Tehran's nuclear programme in return for the easing of sanctions.
Meanwhile, the International Atomic Energy Agency (IAEA) reached an accord with Iran on a "roadmap for cooperation" during a visit to Tehran by the head of the UN watchdog, Yukiya Amano.
"The joint statement that was signed today details a roadmap for cooperation that determines mutual steps to resolve remaining issues," Iran's nuclear chief Ali Akbar Salehi said at a news conference with Amano.
Inspectors to visit Arak
Amano hailed the deal as "an important step" but added "much more must be done", in remarks carried by ISNA news agency.
Salehi said that as a gesture of goodwill, IAEA inspectors would be allowed to visit the heavy water plant in Arak as well as Gachin uranium mine in the south.
At least a year from completion, the Arak reactor is a major source of concern for Western powers who fear the plutonium it will produce as a by-product could provide Iran with a second route for making fissile material for an atom bomb.
Iran has long been adamant it wants to produce isotopes solely for medical and agricultural purposes at the Arak plant.
The IAEA chief's visit was aimed at resolving technical issues linked to the body's role in monitoring Iran's nuclear activities.
Broader questions of how to ensure Iran's nuclear drive is not being used to mask a drive for atomic weapons are being discussed in negotiations between Iran and P5+1 powers -- Britain, France, the United States, Russia and China plus Germany.
In the latest talks, a marathon session in Geneva which ended inconclusively on Sunday, hopes for a deal had soared after top diplomats rushed to join the talks.
But they faded as cracks appeared among world powers when France raised concerns over the heavy water reactor at Arak.
France said the two sides were close to an agreement despite the failure of the Geneva talks.
"We are not far from an agreement with the Iranians but we are not there yet," said Foreign Minister Laurent Fabius.
Responding to criticism that Paris was behind the failure because of its reservations about parts of the deal on the table, he retorted: "France is neither isolated nor a country that follows the herd. It is independent and works for peace."
His comments were echoed by a senior Western diplomat in Brussels who said the talks needed more time.
Tehran denies seeking or ever having sought nuclear weapons, and says such claims are based on faulty intelligence from agencies such as the CIA and Israel's Mossad.
The IAEA in particular wants to visit the Parchin military base, southeast of Tehran, where intelligence evidence suggests Iran may have carried out weaponisation research.
But Salehi and Amano did not mention Parchin as being part of the deal they struck.
Meanwhile, Iran and Britain named non-resident charges d'affaires to each other's capitals, in moves aimed at restoring diplomatic ties severed after the British embassy in Tehran was ransacked in 2011.