World powers were considering the next step after their failure to persuade Iran to allay fears over its nuclear programme, with some observers raising the possibility of further US sanctions.
No new talks were scheduled with Tehran, EU foreign policy chief Catherine Ashton told reporters at the end of two days of talks in Istanbul on Saturday.
"We had hoped to embark on a discussion of practical ways forward, and have made every effort to make that happen. I am disappointed to say that this has not been possible," she added.
Iran's talks with the P5+1 group comprising Britain, China, France, Russia, the United States and Germany had done nothing to allay fears that Tehran might be secretly developing an atomic bomb.
"It remains essential that Iran demonstrates that its nuclear programme is peaceful," Ashton told reporters.
hey had hoped to make progress on a revised version of a nuclear fuel swop proposal and ways to improve transparency through monitoring measures by the UN atomic watchdog, said Ashton.
But "...it became clear that the Iranian side was not ready for this, unless we agreed to pre-conditions relating to enrichment and sanctions," she said in a statement issued on behalf of the six powers.
In London, British Foreign Secretary William Hague said Iran's "refusal to engage" was "extremely disappointing".
French Foreign Minister Michele Alliot-Marie said the conditions Iran had set -- including the lifting of sanctions -- were the reasons the talks had failed.
"This blocked everything," she told reporters in Paris.
Ashton said that while now was the time to take a pause, the door remained opened to future talks -- a sentiment echoed by a senior US diplomat.
"Clearly, the sanctions have had an impact," the diplomat added, speaking on condition of anonymity.
"Clearly, according to public reports, there are signs that the Iranian nuclear programme has slowed. So I think there is time and space for diplomacy," he said.
The slowing of the nuclear programme appeared to be a reference to the effects of the computer virus Stuxnet, which targeted Iranian nuclear centrifuges producing enriched uranium in November.
Israel has said the cyber-attack set back Iran's plans for an atomic bomb by several years. Iran, which denies any such military ambitions, said Thursday the virus had not affected its nuclear programme.
According to a report in the New York Times, Stuxnet was developed by the United States and Israel.
Ahead of the Istanbul talks, US Secretary of State Hillary Clinton said the sanctions already in place against Iran were biting, slowing the Iranian nuclear programme.
For Iran specialist Bruno Tertrais of the Paris-based Foundation for Strategic Research, the US felt they could afford to play a waiting game.
"Since the summer of 2010, the tension has eased," he said.
"The sanctions are starting to be felt and there have been sabotage operations," referring to the Stuxnet cyber-attack.
How things go from here however, is far from clear, said Mohammad Saleh Sedghian, head of the Tehran-based Arabic Centre for Iranian Studies.
"It is very difficult to predict the future of Iran's nuclear case now since many factors can shape its future.
"On one side the Iranian parliament has said that it could take steps obliging the government not to take part in any more talks.
"On the other hand the US could go towards adoption of another set of sanctions against Tehran, which in turn will harden the Iranian position."
According to the New York Times however, Obama could come under pressure to impose fresh sanctions, a view shared by Semiz Idiz, editorial writer at the Turkish newspaper Milliyet.
"I would not be surprised to see the West adopt new sanctions against Iran to force it more towards a compromise," he said.
Iran's nuclear programme has already been the subject of six UN Security Council resolutions, of which four included a range of economic and political sanctions.
On top of those measures, the United States and several other countries have imposed their own sanctions.
AFP/wk
