US negotiator Wendy Sherman and Helga Schmid, the EU's political director, were part of the meetings on Wednesday in the latest round of talks, which are in their final month before a June 30 deadline for a deal with Iran.
Questions arose over whether a deal could be reached on time after US Secretary of State John Kerry broke his leg a day after talks with his Iranian counterpart, Mohammad Javad Zarif, in Geneva over the weekend.
State Department spokeswoman Marie Harf said on Wednesday she was confident Kerry would be "part of these talks at the end."
The sides met for six hours on Saturday trying to overcome obstacles to a final nuclear agreement. Diplomats have said that inspections of Iranian military sites by the International Atomic Energy Agency, the UN watchdog, and access to Iran's nuclear scientists are two of the most contentious issues being addressed in current talks.
Iran is pushing for all sanctions to be lifted once a deal is done.