"The dialogue with the United States took place in a positive climate and was constructive," the ISNA news agency quoted Araqchi as saying after several hours of talks with the US delegation.
"The talks will resume tomorrow (Tuesday) at 9:00 am local time," he added. Senior Iranian and American officials began the two days of direct talks in an urgent effort to find common ground over Tehran's controversial nuclear programme as a July 20 deadline for a lasting atomic deal looms.
For the Islamic republic, the goal is to make a leap towards ending the international sanctions that have battered its economy. Washington and its allies are seeking solid commitments that will ensure Iran's stated desire for a peaceful atomic power programme is not a covert attempt to build a nuclear bomb.