The United States and Iran reported progress in their latest round of nuclear talks on Saturday and agreed to meet again next week as they pursue a deal that could help ease soaring Middle East tensions.

A US official called the talks "positive and productive", and Iran's top diplomat said the two sides will study how to narrow their differences on a range of subjects before next week's fourth round.

The highest-level contact in years between the long-time foes is targeting a new deal that would stop Iran developing nuclear weapons -- an objective Tehran denies pursuing -- in return for relief from sanctions.

"There is still much to do, but further progress was made on getting to a deal," the senior US official said on condition of anonymity, adding that the next talks would be in Europe.