Head of the Atomic Energy Organization of Iran (AEOI) Ali Akbar Salehi and Hossein Fereidoon, special assistance to Iranian President Hassan Rouhani, have joined the countrys team of negotiators in this decisive round of nuclear talks.
AEOI Spokesman Behrouz Kamalvandi said on Tuesday that Mr. Salehi has recovered from a recent surgery and is now in good health.
Since June 17, senior representatives from Iran, the Group 5+1 (Russia, China, the US, Britain, France and Germany) and the European Union have been in Vienna to finalize the text of a comprehensive nuclear deal.
The EU coordinates diplomacy with Iran on behalf of the six nations.
The negotiations climaxed on Saturday with the arrival of the two sides foreign ministers, seeking to hammer out the long-awaited deal before a self-imposed deadline of June 30.
Zarif had left the talks on Sunday night after holding separate meetings with his counterparts from the US, Britain, France and Germany and with European Union's foreign policy chief Federica Mogherini.
The top Iranian negotiator is going to meet US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov during his presence in Vienna on Tuesday.
On Monday, top Iranian negotiators and deputies to foreign minister, Abbas Araqchi and Majid Takht Ravanchi, held meetings with EU deputy foreign policy chief Helga Schmid and US Under Secretary of State for Political Affairs Wendy Sherman.
Iranian officials have announced that if the parties decide to extend the deadline beyond June 30, negotiations will go on for a couple of more days, not months like in the past.
On April 2, Iran and the Group 5+1 (alternatively known as the P5+1 or E3+3) reached a framework nuclear agreement in Lausanne, Switzerland, that provides outlines of a final agreement, known as the Joint Comprehensive Plan of Action (JCPOA).