Speaking to reporters Enrique Mora gave no indication when the talks would resume, but said progress had been made and that the participants would have a clearer idea of how to close a deal when they return.
He added that he expected the international nuclear watchdog and Tehran to reach an agreement on extending a monitoring deal of Iran's nuclear activities that ends on June 24.
Russia's envoy Mikhael Ulyanov told reporters nobody knew when the talks would resume.