The expert-level talks began on Wednesday evening in the Austrian capital, one of the four headquarters of the United Nations.
The two-day talks started on the sidelines of the quarterly meeting of the International Atomic Energy Agency’s (IAEA) Board of Governors.
Hamid Baeedinejad, the director general for political and international affairs at Iran’s foreign ministry, leads the Iranian delegation in the expert-level talks.
And Stephen Clement, who is an aide to the European Union foreign policy chief Catherine Ashton, heads the opposite negotiating team which is made up of technical experts from the six countries (the five permanent UN Security Council members plus Germany).
The expert-level talks come a few days before political directors from the two sides convene a fresh round of high-profile negotiations in Vienna from June 16 to 20.
The negotiations are aimed at drafting a comprehensive deal to resolve the decade-long standoff over Tehran's nuclear energy program.