VIENNA (Reuters) - Experts from Iran and six world powers labored for a fourth day on Thursday to work out exactly how to implement last month's breakthrough deal for Tehran to curb its nuclear program in return for limited sanctions easing.
The length of the closed-door discussions at the Vienna headquarters of the U.N. nuclear watchdog indicated the complexity of the task, not necessarily any major disagreements.
Diplomats said it showed the parties were determined to ensure that there would be no misunderstandings in the implementation of the November 24 interim agreement. It is a "good sign" they are taking their time to get it right, one said.
Iranian officials suggested after the second day of talks on Tuesday that progress was being made but have since declined to comment. Diplomats said the discussions were likely to continue on Friday and might stretch into the weekend.
Experts from Iran, the United States, China, Britain, France, Germany, Russia, the European Union and the U.N. International Atomic Energy Agency (IAEA) attended the talks.
The interim accord, reached after marathon talks in Geneva, is seen as a step towards resolving a decade-old standoff over suspicions that Iran is covertly pursuing a nuclear weapons "breakout" capability, a perception that has raised the risk of a Middle East war. Iran says its atomic work is purely peaceful.
Western diplomats said the talks in Vienna are to hammer out details not addressed at the November 20-24 talks in Geneva.
These include how and when the IAEA, which regularly visits Iranian nuclear sites to check that there are no diversions of atomic material, will carry out its expanded role and other technical issues.
A start to sanctions relief would hinge on verification that Iran was fulfilling its side of the accord, including the suspension of its higher-grade uranium enrichment work, the diplomats said.
The deal was designed to halt Iran's nuclear advances for six months to buy time for negotiations on a final settlement of the dispute. Diplomats say implementation may start in January after technical matters have been settled.
Scope for diplomacy widened after Iran elected the pragmatic Hassan Rouhani as president in June. He had promised to reduce Tehran's international isolation and win relief from sanctions that have severely damaged the oil producer's economy.
(Reporting by Fredrik Dahl; Editing by Alistair Lyon)