The spokesman stressed that "since entering the talks with goodwill, the Iranian delegation has been discussing specific frameworks based on the country's principled positions under international law regarding using nuclear energy peacefully and ending illegal sanctions, demonstrating its seriousness in result-oriented talks aimed at achieving a just, rational, and sustainable agreement."

The U. S. participated in talks with Iranian officials once in Rome and twice in Oman.

The foreign minister of Oman credited the delay to ‘logistical reasons’, but the postponement comes amid new sanctions.

Washington and Tehran have been conducting negotiations over the past month on a deal to curb Iran's nuclear programme in return for the lifting of financial sanctions.