The reluctance from the U.S. to fully lift the sanctions against Iran is the major challenge for the revival of the 2015 nuclear deal, Iranian media Tasnim News Agency quoted an Iranian official as saying on Sunday.

"We believe that whenever the U.S. government ditches the maximum pressure campaign and the European parties show the necessary political will in the negotiations, the road to the immediate achievement of a deal will be opened," the official said, according to the report.