He after arriving to Vieena said: Negotiations reached a critical stage and the Iranian people accept the agreement that is fair, balanced and based on national dignity and the rights of the Iranian people.

Zarif is to negotiate with his American counterpart John Kerry within an hour.

President's special aide Hossein Fereydoun and Head of Atomic Energy Organization of Iran (AEOI) Ali-Akbar Salehi travelled with Zarif.

Iranian foreign minister left the Austrian capital late on Sunday, but his deputies Abbas Araqchi and Majid Takht-e Ravanchi stayed here to continue talks on writing the text of the comprehensive agreement.

In the absence of Zarif, the Iranian negotiators held four rounds of talks with European Union deputy foreign policy chief Helga Schmidt on Monday. The US Undersecretary of State Wendy Sherman was present in one round of those talks, IRNA reports.

Iran, the European Union and representatives of the P5+1 have been holding intensive nuclear talks to reach a final agreement on Iran's nuclear issue.