Top Iranian negotiators and deputies to foreign minister, Abbas Araqchi and Majid Takht Ravanchi, held a meeting with the European Union deputy foreign policy chief, Helga Schmid, on Sunday morning.
They have been holding regular daily meetings in Vienna since June 17 in a push to finalize the text of a comprehensive nuclear deal between Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany).
The EU coordinates diplomacy with Iran on behalf of the six powers.
Experts are also holding tight meetings concurrent with the deputy-level talks.
This fresh round of diplomatic negotiations will continue steadily until the self-imposed deadline of June 30.
Meanwhile, Iranian Foreign Minister Mohammad Javad Zarif will travel to Luxemburg on Monday to meet with his British, French and German counterparts and the European Union's foreign policy chief for talks on the long-awaited nuclear deal.
Araqchi and Takht Ravanchi will also join him in Luxemburg later.
Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) are negotiating to hammer out a lasting accord that would end more than a decade of impasse over Tehran's civilian nuclear program.
On April 2, the two sides reached a framework nuclear agreement in Lausanne, Switzerland, with both sides committed to push for a final deal until the end of June.