Iran and six world powers plan expert-level talks next week to work out details of implementing a breakthrough agreement for Tehran.
The plans are to curb its disputed nuclear programme in return for a limited easing of sanctions.
Officials from Iran and the United States, France, Germany, Britain, China and Russia are to meet on 9 December in Vienna.
The International Atomic Energy Agency will be tasked with verifying that Iran carries out its part of the 24 November interim accord.
Western diplomats said the experts must iron out nitty gritty matters of implementation not addressed in Geneva before the deal can be put into practice.
These include how and when the IAEA will conduct its expanded inspections and other technical issues.
The landmark agreement is seen as a first step towards resolving a decade-old dispute over Iran's nuclear programme that has stirred fears of a new Middle East war.
It was designed to halt Iran's nuclear advances for a period of six months and buy time for negotiations on a final settlement of the standoff.
Diplomats say implementation may start in January after the technical details have been settled.
A diplomatic window opened after the election in June of a relative moderate, Hassan Rouhani, as Iranian president.
He pledged to end Tehran's isolation and win relief from sanctions that have severely damaged the oil producer's economy.
Diplomats and analysts stress that many difficult hurdles remain to overcome.
The hurdles include differences over the scope and capacity of Iran's nuclear project, for a long-term solution to be found.
Under last month's pact, Iran will stop the activity most applicable to producing nuclear weapons.
The activity of enriching uranium to a higher fissile concentration of 20%.
It will also halt installation work at its Arak heavy-water research reactor which, once operating, could yield bomb-grade plutonium.
Highly enriched uranium and plutonium can both form the fissile core of a nuclear bomb.
