Vienna: US Secretary of State John Kerry was due back in Vienna Wednesday for a fresh push with his Iranian counterpart to jumpstart stalled talks over Tehran`s nuclear programme.
Iran and six world powers have six weeks, before a November 24 deadline, to strike a historic deal meant to prevent Tehran from developing nuclear weapons under the guise of its civilian atomic programme.
Kerry, who attempted a similar mission in Vienna before a July deadline which was then pushed back, said Tuesday there was still hard work to be done but that a deal remains achievable.
"I don`t believe it`s out of reach, but we have some tough issues to resolve," Kerry told reporters in Paris after talks with Russian Foreign Minister Sergei Lavrov.
Iranian Foreign Minister Mohammad Javad Zarif struck a similar tone after talks with EU and US officials in Vienna, telling state media that the "notable differences" were "not insurmountable".
"All the issues are linked and we need to reach an agreement that covers all issues... Nothing is agreed until everything is agreed," Zarif said late Tuesday.
Kerry refused to be drawn on whether -- as suggested by many experts -- Iran and the six powers might push back the target date.
"We need to continue to have some serious discussions, which we will, and we`ll see where we are," he said.
"I don`t think anything is served by a lot of speculation at this point in time."
But Russia`s Lavrov, whose country together with the US, China, Britain, France and Germany forms the P5+1 group, said Tuesday in Paris that the November deadline was not "sacred".
"We aspire to get a result by that date but I am convinced by the principle that it is not artificially-set deadlines but the essence of the deal, the quality of the deal (that counts)," Lavrov said, according to Interfax.
Zarif too appeared to indicate that another extension might be needed in order to discuss what he called "serious and innovative" -- but unspecified -- "new methods".
"These talks will take time however and it is possible that more time might be needed to discuss these solutions," he told state television.Iran, reeling from sanctions pressure, denies wanting the bomb and wants to expand its nuclear programme in order, it says, to generate electricity and help cancer patients.
But the six powers are pressing Tehran to reduce in scope its activities in order to make any dash to make a weapon all but impossible, offering in return sanctions relief.
Last November, the two sides agreed an interim deal and set a July 20 target to agree a lasting accord, but after several rounds of intensive negotiations the deadline was extended to November 24.
Progress appears to have been made on changing the design of a new reactor at Arak so that it produces less weapons-grade plutonium, as well as on enhanced UN inspections and on the fortified Fordo facility.
The main bone of contention however remains Iran`s enrichment capacity, a process rendering uranium suitable for power generation but also, at high purities, for a nuclear weapon.
Other problem areas include the pace at which sanctions would be lifted, the timeframe that an accord would cover and a troubled UN probe into past suspect "military dimensions" of Iran`s activities.Many analysts have begun to believe that the deadline might be extended again, possibly locking in something on Arak and Fordo, into a so-called "Interim Plus" deal.
"A fully-fledged agreement by November 24 no longer appears likely. What is still possible is a breakthrough that could justify adding more time to the diplomatic clock," Ali Vaez from the International Crisis Group told AFP.
Speculation about a possible extension has been stoked by comments from Iranian officials, including President Hassan Rouhani.
"Our will is that in 40 days the matter will be resolved but if other things happen and we are not able to solve all the problems, the two camps will find a solution," Rouhani said on state television on Friday.
A one-day meeting involving Iran and all six powers was scheduled for Thursday.