A top Iranian nuclear negotiator expressed hope Sunday a deal with world powers could be implemented within a month, but said technical talks on the matter are proceeding slowly, Mehr news agency reported.

The deal, signed in November, saw Iran suspend parts of its contested nuclear programme for six months in return for limited sanctions relief while a longer term agreement is hammered out.

"If expert-level talks are fruitful, a date will be decided which I guess will be at the end of January" for the deal to be implemented by, said Abbas Araqchi, a deputy foreign minister, in comments run by Mehr.

His remarks came on the eve of the third round of technical talks between Iranian representatives and the so-called P5+1 group of world powers -- the United States, Britain, France, China and Russia plus Germany.

The talks are aimed at setting a framework to implement the nuclear deal clinched in Geneva on November 24, which seeks to buy time to thrash out a diplomatic solution to a decade-long standoff over Iran's nuclear ambitions.

But Araqchi said the talks were "not that easy."

"The negotiations are proceeding slowly as there are misunderstandings over interpretation of some elements of the accord," he said.

Under the deal, Iran agreed to roll back or freeze parts of its nuclear drive for six months in exchange for modest sanctions relief and a promise by Western powers not to impose new measures.

The first round of technical talks in Vienna were interrupted in early December when Iranians walked out after Washington expanded its existing sanctions blacklist against Tehran.

The second round was suspended as the Christmas holidays approached.

When the sides agree on how to implement an accord, Iran and world powers will open negotiations to hammer out a comprehensive deal to allay Western suspicions that Tehran's nuclear drive masks military objectives.

Iran has repeatedly denied it is trying to develop atomic weapons, saying its programme is for peaceful applications of generation energy and producing medical isotopes.