Talks between Iran and world powers on implementing last month's nuclear deal will resume Thursday in Geneva, a spokesman for EU foreign policy chief Catherine Ashton, and Tehran, said Wednesday.

"The technical talks will be resumed tomorrow and continue until Friday" in Geneva, Michael Mann told AFP via email.

The experts held four days of talks in Vienna last week but the Iranians walked out after Washington expanded its sanctions blacklist against Tehran.

Iran's state broadcaster quoted deputy foreign minister Abbas Araqchi as saying the two days of talks could be extended to the weekend.

He said Tehran was prepared to continue the talks after Ashton "made the assurance that the world powers, particularly the United States, will continue the talks in goodwill... and that they are serious about implementing the deal".

Under the landmark November 24 accord struck in Geneva, Iran agreed to roll back parts of its nuclear programme for six months in exchange for modest sanctions relief and a promise not to impose new sanctions.

But the United States last week put a dozen overseas companies on a blacklist for evading its sanctions, angering Tehran even though Washington said the new measures did not constitute new sanctions.

Tehran said the measures were "against the spirit" of the November 24 deal.

Foreign Minister Mohammad Javad Zarif expressed Iran's "discontent" in a phone call with US Secretary of State John Kerry, Iranian news agency Fars reported on Monday. The State Department confirmed the call took place.

During the six-month nuclear freeze, which has not started yet, Iran and the powers aim to hammer out a long-term comprehensive accord to end once and for all the standoff over Iran's nuclear programme after a decade of failed attempts and rising tensions.

Iran denies wanting nuclear weapons, but many in the international community suspect otherwise, and neither Israel -- widely assumed to have nuclear weapons itself -- nor Washington have ruled out military action.

The six powers, known as the P5+1, are the United States, China, Russia, Britain, France and Germany.

Araqchi had told Belgian newspaper Le Soir on Tuesday that after speaking to Ashton -- the P5+1's chief negotiator -- Tehran had "decided to resume" the talks.

Diplomats told AFP that the talks last week in Vienna were heavy-going as the parties sought to work out a carefully calibrated process of when sanctions would be eased, when the nuclear freeze would start and how it would be verified.

They insisted, however, that the discussions were not any harder than expected and that the differences would eventually be ironed out.

Iran's nuclear freeze will be verified by the International Atomic Energy Agency, the UN nuclear watchdog.

A source close to Tehran's negotiating team told the ISNA news agency on Wednesday that IAEA experts could also "join the talks if necessary".