Talks to try to save the Iran nuclear deal have been held amid rising tensions over tankers in the Gulf.
After meeting officials from Britain, France, Germany, Russia and China in Vienna, a senior Iranian official said the atmosphere had been "constructive".
Tensions have soared since the United States withdrew from the 2015 accord last year and reimposed sanctions.
In recent weeks, Iran and Britain have seized a tanker each - putting further pressure on the 2015 accord.
Iran has also admitted breaching restrictions on its production of enriched uranium, used to make reactor fuel but also potentially nuclear bombs.