Vienna: Iran and the US still aim to strike a mammoth nuclear deal by a November 24 deadline, a US official said after talks involving US Secretary of State John Kerry that yielded no apparent major breakthrough.
"We have not discussed an extension. We believe in keeping the pressure on ourselves," the senior US State Department official said after six hours of "very intense" discussions in Vienna.
"If you take the pressure off yourself, then you never have to make hard decisions. Deadlines help people to make hard decisions, and there are hard decisions to be made here. And we must."
She added: "Everyone has been working incredibly hard... these are incredibly complex negotiations, the detail is extraordinary.
"Until everything is agreed, nothing is agreed, and you can get 98 per cent of the way, and the last two percent may kill the entire deal."
It was unclear whether Kerry would resume his talks with Iranian Foreign Minister Mohammad Javad Zarif today, when Zarif was scheduled to meet with negotiators from six world powers in the Austrian capital.
Iran and the six world powers have less than six weeks, until November 24, to strike a comprehensive accord meant to prevent Tehran from developing nuclear weapons under the cover of its civilian atomic programme.
Iran, reeling from sanctions, denies seeking to build the atomic bomb and says it wants to expand its nuclear programme in order to generate electricity and help cancer patients.
But the powers -- the United States, France, Britain, Russia, China and Germany -- are pressing Tehran to reduce its activities in order to make any dash to make a weapon all but impossible, offering sanctions relief in return.
Last November, the two sides agreed an interim deal and set a July 20 target to agree a lasting accord, but after drawn out talks they gave themselves four more months.
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 thorny areas include the pace at which sanctions would be lifted, the timeframe that an accord would cover, and a stymied UN probe into past suspect "military dimensions" of Iran's activities.