Experts from Iran and six world powers are launching a new round of negotiations focused on reaching a deal that curbs Iran's nuclear program.
Diplomats said ahead of Wednesday's meeting (local time) that progress is being made but significant gaps remain on a main document and technical annexes ahead of an end-of-June deadline.
Iran's team is led by Deputy Foreign Minister Abbas Araghchi. EU official Helga Schmidt is heading the other side. Senior officials from the U.S., Russia, China, Britain, France and Germany may join in later.
The deal aims for strict limits on Iranian nuclear capabilities that could be used to make weapons. Tehran denies any interest in such arms but is negotiating for a lifting of sanctions.
The diplomats demanded anonymity because they are not authorized to discuss the talks.