“Talks have now reached sensitive and complicated phases and it is necessary that [the talks] continue at higher levels,” Abbas Araqchi told reporters in Geneva, where the nuclear talks are underway, on Friday.

“Fortunately, expert-level talks about the text [of a possible agreement] have made good progress between experts from both sides,” he said, adding that it was too early, however, to predict if the talks would reach a conclusion on Friday.

The talks about Iran’s nuclear energy program started between Iran and the six world powers -- the US, France, Britain, France, Russia, China and Germany -- in Geneva on Thursday.

Araqchi also stated that Iran’s Foreign Minister Mohammad Javad Zarif is to attend tripartite talks with EU foreign policy chief, Catherine Ashton, and US Secretary of State John Kerry.

He added that Zarif is also to meet with British Foreign Secretary William Hague, French Foreign Minister Lauren Fabius and German Foreign Minister Guido Westerwelle.

Araqchi reaffirmed Iran’s right to enrich uranium, but said Tehran is ready to “negotiate about the dimensions, type and level of enrichment.”

Kerry arrived in Geneva on Friday to join Iran’s foreign minister and Ashton, who is representing six world powers in the nuclear talks.

Earlier in the day, Westerwelle said he believes that an important moment has arrived in the negotiations with Iran over its nuclear energy program.

For his part, Fabius said Iran and six world powers have made progress in the course of their nuclear talks, noting that no deal has been struck between the two sides yet.