It is expected that their discussions will drag beyond midnight.

Earlier in the day, Zarif met French Foreign Minister Laurent Fabius and special envoy of Russian foreign minister.

In the meantime, representatives from P5+1 group of world powers and EU convened as negotiators are approaching the newly set deadline of July 13, IRNA reports.

Zarif's deputies also held talks with EU and US envoys separately.

Meanwhile head of the Atomic Energy Organization of Iran (AEOI) Ali Akbar Salehi voiced strong optimism about reaching a final deal with the Group 5+1 (the US, Russia, China, France and Britain plus Germany).

Asked about the latest developments in the nuclear talks between Iran and the six major world powers in Vienna, Salehi said, "Good news. It couldn't have been better."

Salehi had also on Friday voiced his satisfaction with the ongoing trend of the nuclear negotiations between Tehran and the world powers in Vienna, and said that there is still a strong possibility for striking a final agreement.

"There is a high chance for agreement in the Austrian capital," Salehi told reporters in Vienna on Friday.

He underlined that the negotiations are making progress as the two sides are doing their best to narrow down the differences, FNA reports.