Deputy foreign ministers from Iran, Abbas Araqchi and Majid Takht Ravanchi, had a meeting with the US delegation, led by Under Secretary of State for Political Affairs Wendy Sherman.
The Montreux talks also includes Deputy Secretary General for the European Union's External Action Service Helga Schmid.
A plenary session involving Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) will be held on March 5.
Elsewhere in Switzerland, Iranian Foreign Minister Mohammad Javad Zarif is in Geneva, where he addressed the high-level segment of the 28th session of the United Nations Human Rights Council.
The top Iranian diplomat is planned to meet US Secretary of State John Kerry in Geneva.
Iran and the Group 5+1 (also known as the P5+1 or E3+3) are in talks to hammer out a final agreement to end more than a decade of impasse over Tehran’s civilian nuclear energy program.
The two sides held bilateral and multilateral negotiations in Geneva earlier in February to narrow the remaining differences ahead of a deadline for a final agreement by July 1.