Top Iranian negotiators and deputies to foreign minister, Abbas Araqchi and Majid Takht Ravanchi, the European Union deputy foreign policy chief Helga Schmid and US Under Secretary of State for Political Affairs Wendy Sherman held a long meeting in Vienna on Thursday night.
The 6-hour session stretched into the early hours of Friday.
Deputy and expert-level meetings will go on in the Austrian capital today, after Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) agreed on Tuesday to continue the negotiations for 7 more days beyond an end-June deadline in the hope of clinching a final nuclear deal.
Separately, Iranian Foreign Minister Mohammad Javad Zarif, who is in Vienna as head of the Iranian team of nuclear negotiators, met with Austrian President Heinz Fischer on Friday.
Austria has announced it is an honor for the European country to host the high-profile nuclear talks between Iran and the six world powers.