Zarif arrived in Vienna on Saturday morning after Kerry who had arrived in the Austrian capital on Friday night.

The two foreign ministers had previously held two rounds of talks once in New York and another time in Geneva to discuss drafting the comprehensive deal and bridging the differences, IRNA reports.

Foreign Ministry Deputies Abbas Araqchi and Majid Takht-e Ravanchi have also been in Vienna since last Wednesday to hold the eighth round of nuclear talks with their EU and US counterparts on drafting of the final deal.

Araqchi says the two sides have made some progress but many important issues remain unsolved that need to be decided by foreign ministers.

Some hours later, Iran’s chief negotiator in nuclear talks with the group P5+1 and the Deputy of Foreign Minister Seyyed Abbas Araghchi told Al-Alam News Network correspondent that “Changing Viewpoints of some P5+1 countries after Lausanne Negotiations caused harder works.”

Iran and the six world powers – the United States, Britain, France, Germany, Russia and China – have set June 30 as their deadline for reaching a comprehensive nuclear deal.