In particular the two-day Vienna meeting, due to begin at 1400 GMT, will seek to nail down the start date of Iran's promised six-month nuclear freeze, how this will be monitored and when sanctions will be eased. (Agencies)
After the talks with representatives from the United States, China, Russia, Britain, France and Germany -- the P5+1 -- Iranian officials will then meet just with the International Atomic Energy Agency on Wednesday.
In a major diplomatic breakthrough in Geneva on November 24, Tehran committed to limit uranium enrichment to low fissile purities for six months and not to make further advances at its Fordo, Natanz and Arak facilities.
Iran will also neutralise its stockpile of medium-enriched uranium -- which is easy to convert to weapons-grade – and allow more intrusive IAEA inspections.
Iran's envoy to the IAEA, Reza Najafi, told reporters on November 29 that he expected the implementation of the deal to begin "either at the end of December or the beginning of January".
The measures will lengthen the time Iran would need to develop nuclear weapons -- if it chose to -- and the deal aims to build trust while a longer-term "comprehensive" accord is negotiated.
Israel however, widely believed to have nuclear weapons itself and which has refused to rule out bombing Iran, has sharply criticised the Geneva deal, with Prime Minister Benjamin Netanyahu calling it a "historic mistake".
Netanyahu said in Washington yesterday that Israel shared US President Barack Obama's "preference" to pursue diplomacy "but for diplomacy to succeed, it must be coupled with powerful sanctions and a credible military threat".
The deal, coupled with Washington's reluctance to take military action against the Tehran-backed Syrian regime, has also irked mostly Sunni Gulf states that view Shiite Iran as a serious threat.
In particular the two-day Vienna meeting, due to begin at 1400 GMT, will seek to nail down the start date of Iran's promised six-month nuclear freeze, how this will be monitored and when sanctions will be eased.