A year-and-a-half of nuclear talks between Iran and major powers were creeping towards the finish line yesterday as negotiators wrestled with sticking points including questions about Tehran’s past atomic research.

Iran is in talks with the US and five other powers – Britain, China, France, Germany and Russia – on an agreement to curtail its nuclear programme in exchange for relief from economic sanctions.

“We are coming to the end,” said a senior Western diplomat, who added there was no plan to carry on for long past next Tuesday.

US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif seemed to be reading from the same script as they spoke to reporters before a meeting with their top aides yesterday .

“We are making progress,” Kerry said. “We have a lot of work to do. There are some tough issues, but genuine effort by everybody.”

Zarif added: “I agree. We are all trying very hard in order to be able to move forward and we have made some progress. There are still tough issues to discuss.”

Still, all sides say a deal is within reach. US, European and Iranian officials, including US Under Secretary of State Wendy Sherman and Iranian deputy foreign ministers Abbas Araqchi and Majid Takhteravanchi, held a six-hour negotiating session that ended at 3am yesterday morning, a senior US official said.

Russia’s chief negotiator Sergei Ryabkov said the text of the agreement was more than 90 per cent complete. Chinese Foreign Minister Wang Yi voiced confidence that the parties would reach a mutually acceptable accord.

The negotiators missed a June 30 deadline for a final agreement, but gave themselves till July 7, and foreign ministers not already in Vienna are due to return tomorrow for a final push. A deal, if agreed, would require Iran to severely curtail uranium enrichment work for more than a decade to ensure it would need at least one year’s “breakout time” to produce enough highly enriched uranium for a single weapon, compared with current estimates of two to three months.

Western and Iranian officials said there were signs of a compromise emerging on one of the major sticking points: access to Iranian sites to monitor compliance with a future agreement. Another potential compromise relates to Iran’s low enriched uranium stockpiles. Western and Iranian diplomats said Tehran was considering shipping most of the stockpile out of the country, something Tehran had previously ruled out. A senior Iranian official in Vienna said Iran would sign up to an IAEA inspection regime called the Additional Protocol, which would be provisionally implemented at the start of a deal and later ratified by Iran’s Parliament.

The Protocol allows IAEA inspectors increased access to sites where they suspect nuclear activity is taking place, but US officials say it is insufficient because Iran has in the past stalled by dragging out negotiations over access requests.

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