Meanwhile, Iranian President Hassan Rouhani Saturday urged world powers not to miss an "exceptional opportunity" to reach an agreement in their ongoing nuclear talks in Geneva.
 

“I hope that the P5+1 group make the most out of this exceptional opportunity that the Iranian nation has offered to the international community, so that we can reach a positive result within a reasonable time frame," he was quoted as saying by official IRNA news agency.
 

If world powers and Iran fail to reach a hoped-for deal Saturday over Tehran's disputed nuclear program, a new round of talks will be held in seven or 10 days, Iran's Foreign Minister Mohammad Javad Zarif was quoted as saying by Iranian news agency IRNA.
 

Zarif's comments followed initial optimism after U.S. Secretary of State John Kerry and his Russian, British, French and German counterparts all rushed to Geneva to lend weight to the negotiations aimed at ending the decade-long dispute over Iran's nuclear program.
 

But on the unscheduled third day of talks Saturday, cracks seemed to emerge among the group of world powers after French Foreign Minister Laurent Fabius raised concerns and said Paris had not accepted an initial draft of the deal.
 

"As I speak to you, I cannot say there is any certainty that we can conclude," Fabius said on France Inter radio, stressing that Paris could not accept a "sucker's deal.”
 

His pointed remarks hinted at a rift brewing within the Western camp. A Western diplomat close to the negotiations said the French were trying to upstage the other powers.
 

"The Americans, the EU and the Iranians have been working intensively together for months on this proposal, and this is nothing more than an attempt by Fabius to insert himself into relevance late in the negotiations," the diplomat told Reuters news service, speaking on the condition of anonymity.
 

The main sticking points appeared to include calls for a shutdown of an Iranian reactor that could eventually help produce weapons-grade nuclear fuel, the fate of Iran's stockpile of higher-enriched uranium and the nature and sequencing of relief from economic sanctions sought by Tehran.
 

Kerry avoided the media on Saturday before engaging in another two hours of intensive talks with Zarif and European Union foreign policy chief Catherine Ashton. The three met for five hours on Friday night.
 

British Foreign Secretary William Hague had said the talks have achieved "very good progress" but much more needed to be agreed and it was unclear if this would happen by the end of the day.
 

"We are very conscious of the fact that real momentum has built up in these negotiations," he told reporters. "So we have to do everything we can to seize the moment."
 

Foreign ministers from all five permanent U.N. Security Council members — Britain, China, France, Russia and the United States — and Germany took part in Saturday's talks with Zarif.
 

But it is only the Americans and Iranians, whose estranged countries have not had formal diplomatic ties for more than three decades, with the power to make or break an agreement on Iran's contested nuclear ambitions.
 

The fact that any deal might be feasible after a decade of feuding rather than genuine negotiations between Iran and the West highlights a striking shift in the tone of Tehran's foreign policy since the landslide election in June of moderate Rouhani as president.
 

The powers remain concerned that Iran is continuing to amass enriched uranium not for future nuclear power stations, as Tehran says, but as potential fuel for nuclear warheads.
 

They are searching for a preliminary agreement that would restrain Iran's nuclear program and make it more transparent for U.N. anti-proliferation inspectors. In exchange, Tehran would obtain phased, initially limited, relief from punitive sanctions throttling the economy of the giant OPEC state.
 

The goal now is to take a big first step towards resolving a protracted dispute rife with political baggage and legal complexities and to thereby arrest a drift towards a major new war in the world's most volatile region.
 

"We're working hard," Kerry told reporters on Friday night.
 

Iran spelled out one major bone of contention. A member of its negotiating team, Majid Takt-Ravanchi, told Mehr news agency on Friday that Western powers should consider easing oil and banking sanctions during the first phase of any deal.
 

The powers have offered Iran access to Iranian funds frozen abroad for many years but ruled out any broad dilution of the overall sanctions regime in the early going of an agreement.
 

Diplomats said that even a breakthrough this weekend would be only the start of a long confidence-building process towards a permanent resolution of concerns about Iran's nuclear quest.
 

But they said the arrival of Kerry, Fabius, Hague, German Foreign Minister Guido Westerwelle, Russian Foreign Minister Sergei Lavrov and the expected appearance of Chinese Foreign Minister Wang Yi had signaled that the six powers could be closer to an elusive pact with Iran than ever before.
 

Kerry arrived on Friday from Tel Aviv after what appeared to be a tense meeting with Israeli Prime Minister Benjamin Netanyahu, who rejected any budding compromise with Iran.
 

Netanyahu warned Kerry and his European counterparts that Iran would be getting "the deal of the century" if they carried out proposals to grant Tehran temporary respite from sanctions in exchange for a partial suspension of, and pledge not to expand, its enrichment of uranium for nuclear fuel.
 

Israel, which is believed to have the Middle East's only nuclear arsenal and regards its arch-enemy Iran as a mortal threat, has repeatedly mooted possible military action against Tehran if it did not mothball its entire nuclear program.
 

Iran dismisses such demands, citing a sovereign right to a nuclear energy industry and most diplomats concede that, with Tehran having exponentially expanded nuclear capacity since 2006, the time for demanding a total shutdown has passed.
 

But Fabius said the security concerns of Israel and some Arab neighbors of Iran still "have to be taken into account.”