Iranian and American foreign ministers held their second and third rounds of talks, IRNA reported.
Mohammad Javad Zarif and his US counterpart John Kerry met for the second and third times on Friday evening and night.
The first meeting between Zarif and Kerry was held in the Austrian capital on Thursday.
The Iranian and US foreign minister focused more on the Joint Comprehensive Plan of Action (JCPOA) and the nuclear agreement reached between Tehran and the six world powers (the US, Russia, China, France, Britain and Germany).
Zarif left Tehran for Vienna on Thursday to attend a two-day meeting on the Syrian crisis in Vienna upon an invitation by the western countries and the European Union (EU).
Zarif's deputy Seyed Abbas Araqchi and the foreign ministry's director general for political affairs accompany the Iranian foreign minister during his visit to Vienna.
The foreign ministers of 15 countries and Chinese deputy foreign minister attended the Vienna-II conference on Syrian crisis on Thursday and Friday.