TEHRAN - Tehran is ready to allow nuclear inspectors access to its Marivan military site, an Iranian official said Saturday, a facility long suspected of being used to develop explosive weapons. The declaration comes as Iran and six world powers hold talks in Vienna to reach a lasting agreement on Tehran’s disputed nuclear programme before November 24.

Such a deal, after 12 years of rising tensions, is aimed at easing fears that Tehran will develop nuclear weapons under the guise of its civilian activities - an ambition the Islamic republic has always fiercly denied. The Marivan site, close to the Iraqi border, was mentioned in a 2011 report by the International Atomic Energy Agency (IAEA) on Iran’s alleged pursuit of nuclear weapons. The UN agency suggested at the time that ‘large scale high explosive experiments’ may have been carried out at the complex. Britain, China, France, Russia, the United States and Germany have been locked in talks with Iran since February after an interim accord gave it some relief from economic sanctions in return for nuclear curbs.

‘We are ready to allow the IAEA controlled access to the Marivan site,’ Behrouz Kamalvandi, spokesman for Iran’s Atomic Energy Organisation, was quoted as saying by the IRNA news agency. He said the IAEA’s view of Marivan was based on ‘false’ information. IAEA spokeswoman Gill Tudor said the watchdog ‘will discuss the offer’ with Tehran.

‘The situation regarding a visit to the Marivan region is not as simple as that conveyed by Iran,’ she told AFP. As well as Marivan, IAEA inspectors are also interested in the Parchin military base, where they suspect tests that could be applied to a potential nuclear site have been carried out. Iran has so far denied access to Parchin. Moreover, US Secretary of State John Kerry said Saturday ‘serious gaps’ remained in talks between Iran and world powers in Vienna two days before a deadline to strike a nuclear deal. ‘We’re working hard,’ Kerry said, ‘and we hope we’re making careful progress, but we have big gaps, we still have some serious gaps, which we’re working to close.’ Speaking as he met German counterpart Frank-Walter Steinmeier, Kerry said he would ‘not say anything substantive about the discussions while they’re going on, but a lot of serious work is going on by a lot of people.’

Kerry, who on Friday postponed a trip to Paris to remain in Vienna, was due to meet Iranian Foreign Minister Mohammad Javad Zarif on Saturday afternoon, their fourth meeting in three days. Steinmeier, arriving in the Austrian capital earlier Saturday, said that the final weekend of talks, after months of negotiations, was a ‘moment of truth’.

At stake is a historic deal in which Iran would curb its nuclear activities in exchange for broad relief from years of heavy international economic sanctions. It could end a 12-year standoff with the West that has even raised the threat of Israeli military strikes against Iranian nuclear facilities. ‘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 make concessions.

The differences were such that Britain and Iran have raised the possibility - as expected by many analysts - that a final deal would not be reached by Monday’s deadline, and that the negotiations could be extended. Kerry said in Paris this week that no such extension - which could include a new interim deal - was being discussed. An earlier one was extended in July by four months.

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 by November 24. Such a deal is aimed at easing fears that Tehran will develop nuclear weapons under the guise of its civilian activities. The Islamic Republic hotly denies such an aim and insists its programme is entirely peaceful. 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 and his French counterpart Laurent Fabius also joined the talks on Friday. Both have since left but were expected to return. It was unclear when or whether Russian Foreign Minister Sergei Lavrov, a key player in the talks, might also arrive. Earlier this week the head of the Russian delegation said Lavrov would come only if there was serious progress. Lavrov said from Moscow on Friday that ‘all the elements are already on the table’ for a deal and that all that was missing was ‘political will’. Kerry on Friday ‘updated’ Lavrov by phone. Kerry has also talked with the foreign ministers of several Gulf States and with those of Turkey and Canada, aides said.