Iranian Foreign Minister Mohammad Javad Zarif
Iranian Foreign Minister Mohammad Javad ZarifReuters

Six world powers and Iran groped on Saturday for ways to bridge wide gaps in marathon nuclear negotiations two days ahead of a
November 24 deadline.

At stake in the Austrian capital Vienna is an historic deal in which Iran would promise to curb its nuclear activities in exchange for broad relief from years of heavy international economic sanctions.

US Secretary of State John Kerry was consulting by phone Saturday with his international partners as well as colleagues back in the United States, aides reported, after Washington said "serious gaps" remained in the talks.

Iranian sources said Iranian Foreign Minister Mohammed Javad Zarif would meet Kerry later Saturday for a fourth round of talks in three days, but there was no immediate confirmation of this from the US State Department.

"The gap remains big...there now needs to be a political decision," an Iranian source told AFP on condition of anonymity, putting the onus on the world powers to apparently bend to Iranian demands to be left with enough centrifuges to build 38 atomic bombs per year.

The United States also said hurdles remained high, despite reports that US President Barack Obama has been raising the centrifuge ceiling for Iran, and reports he intends to bypass Congress to reach a deal, which led 43 angered Senators to write Obama for clarification last Wednesday.

"We are running against the clock. Obviously, the deadline is Monday, and our folks there are working furiously to meet it...serious gaps do remain," White House spokesman Eric Schultz said in Washington. He warned Washington would not settle for a bad deal.

The gaps were so wide that Britain and Iran have raised the possibility that a final deal would not be reached by Monday's deadline, and that the negotiations could be extended as has already been done for a previous interim deadline.

Iran demands "compromise"

The United States, Russia, China, Britain, France and Germany have been locked in talks with Iran since February to turn an interim accord reached a year ago into a lasting agreement.

The Islamic Republic hotly denies its nuclear program is meant to build a nuclear weapon, even though the International Atomic Energy Agency (IAEA) has revealed Iran is not abiding by the interim conditions in refusing to answer questions on the military aspects of its program.

Likewise, a former head of the IAEA revealed this month that Iran may have five times more advanced uranium centrifuges than previously thought, making the danger that Iran would be able to quickly develop a nuclear weapon all the more pressing.

A source close to the Iranian delegation told AFP the negotiators aimed for something short of a comprehensive nuclear agreement, seeking instead a deal on "a general framework" whose details would be filled in later.

"There is no other scenario possible at this stage," the source added.

British Foreign Secretary Philip Hammond had raised the possibility of a delay even if Kerry had said he intended to seal a deal by the deadline. Hammond, who left Vienna on Friday, said there was still a "very significant gap," while French Foreign Minister Laurent Fabius called on Iran to "seize this opportunity."

Aides said Fabius returned to Paris on Saturday but would be back in Vienna on Sunday.

German Foreign Minister Frank-Walter Steinmeier was due for talks in Vienna with Kerry, US officials said. Zarif was also to meet the German top diplomat, Iranian sources added.

Russian Foreign Minister Sergei Lavrov, a crucial player, said from Moscow that "all the elements are already on the table" for a deal and that all that was missing was "political will."

Kerry later "updated Foreign Minister Lavrov on the state of negotiations" by phone, the US official said.

Iran said it believes that the onus is on the side of the world powers to compromise to its demands. Zarif and President Hassan Rouhani both warned the powers not to sink the talks with "excessive demands."

Iranian officials in the past have called the question of Iran's uranium centrifuges a "trivial issue" that shouldn't stop talks.

Some areas under discussion appear provisionally settled in what would be a highly complex deal that would run for many years, even decades.

But two key issues remain: enrichment - a process that renders uranium suitable for energy uses but also, at high purities, for a weapon; and the pace of the lifting of sanctions.

Iran wants to massively ramp up the number of enrichment centrifuges - in order, it claims, to make fuel for a fleet of future reactors - while the West wants them dramatically reduced.

With Monday's deadline for a lasting agreement fast approaching, Israel has been urging the six world powers not to give in to Iranian demands and leave it with break-out capability by which it could quickly create an atomic bomb.

AFP contributed to this report.