The high representative of the European Union (EU) for foreign affairs and security policy said on Saturday that six world powers could not get any positive outcome from their nuclear negotiations with Iran.
"This is not the conclusion I'd hoped for," European Union foreign policy chief Catherine Ashton said at the conclusion of the talks in Istanbul on Saturday.
Catherine Ashton, heading the P5+1 (five permanent members of the UN Security Council including the United States, Russia, China, Britain and France plus Germany) delegation, said the delegation aimed to have a detailed and constructive meeting with Iran however Iran was not ready.
"We'd hoped to embark on a discussion of practical ways forward and have made every effort to make that happen," she added. "I am disappointed."
An aide to Iran's chief negotiator Saeed Jalili told Reuters that the talks would resume, even if the timing and venue were still undecided. However, Ashton said further talks depended on a more constructive approach from Tehran.
"The process can go forward if Iran chooses to respond positively," she said. "The door remains open. The choice remains in Iran's hands."
"The process can go forward if Iran chooses to respond positively. We now wait to hear...whether Iran will respond on reflection," she told reporters in Istanbul.
The new round of talks on Iran's nuclear program took place in Istanbul between Iran and five permanent members of UN Security Council and Germany (5+1) on Friday and Saturday.
Saeed Jalili, the secretary of Iran's Supreme National Security Council, chaired the Iranian delegation in the meeting hosted by Turkey.
The first meeting between Iran and P5+1 took place in Geneva, Switzerland in October 2009.
Iran demands respect to its nuclear rights
Jalili said after the talks ended that any agreement would have to be based on Iran's right to pursue enrichment.
Jalili said there was need for a common reason and judgement in order to benefit from negotiations.
"When something other than common judgement and reason is used, this is not dialogue but an instruction," Jalili told a press conference in Istanbul.
Jalili said if they could make progress on cooperation in common interests, the negotiations could then bear fruit.
The chief negotiator said the Iranian delegation came to Istanbul with a positive perspective and practical methods, and Iran's potential could not be denied and other countries could cooperate with his country in many areas.
Any accord between Iran and world powers over its nuclear programme should be based on Tehran's right to nuclear technology, including uranium enrichment, Iran's chief negotiator Saeed Jalili said on Saturday.
"Any kind of talks and cooperation, as I underlined during the talks with Mrs Ashton, should be based on respecting the nations' rights... including Iran's right to nuclear technology," he said, specifying Iran;s right to a nuclear fuel cycle and uranium enrichment.
"I think for the purposes of these talks, Iran came with its pre-conditions very firmly in its mind and what it has gone away with is a total understanding that those are not acceptable," Ashton told reporters.
Iran's nuclear standoff with the West has escalated in the past year, with the United Nations imposing new sanctions and Western states rejecting a revised proposal for Iran to swap some of its fuel abroad as too little, too late.
Ashton had outlined a possible revised offer for a nuclear fuel swap that would entail Iran handing over a large chunk of its stockpile of low enriched uranium. No offer was made as Iran's preconditions included the suspension of economic sanctions, a Western diplomat said.
The powers want to prevent Tehran from accumulating enough material for a nuclear weapon while negotiations proceed on a broader solution to the crisis.
The inconclusive end to a two-day meeting between six world powers and Iran over its nuclear programme was "disappointing", but there was no breakdown in the talks, a senior U.S. official said on Saturday.
Talking to journalists after the talks ended without any concrete result, or even agreement to meet again, the official said "serious differences remained".
During the talks, Iran had refused a request to hold a bilateral with the U.S. delegation headed by Under-Secretary for Political Affairs Bill Burns.
Six world powers are willing to pursue a diplomatic solution with Iran on its nuclear programme but the choice is for Tehran to make, the official said.
The official said: "There are signs that Iran's nuclear programme has slowed so there is time and space for diplomacy ... (We) hope the Iranians recalibrate and provide an opening for diplomacy."
The official also said the big powers -- the United States, Britain, France, Russia, China and Germany -- were "quite united in our purpose"
U.S. Secretary of State Hillary Clinton raised the possibility earlier this week of further increasing such pressure, telling U.S. network ABC the Obama administration may propose new unilateral measures against Iran.
But some analysts say it is unlikely that the U.S.-led drive to isolate Iran and its leaders, who use the nuclear programme to rally nationalist support at home, will make the country back down over its atomic activities soon.
Any U.S. push to again tighten such pressure on Iran may also anger Russia, which voted for a fourth round of U.N. sanctions last June, but which criticised subsequent unilateral steps by the United States and the European Union.
Western officials and experts say the sanctions are hurting the Iranian economy, even though a higher oil price may blunt the impact.