Speaking with CNN’s Senior International correspondent Frederik Pleitgen in Tehran Sunday, Baghaei said the exchange of messages continued through Pakistani mediators.

“The main problem of negotiating with this administration is that you have to face so many changing positions, moving the goal posts, different statements, contradictory remarks by different officials, so it makes the whole process very cumbersome,” Baghaei said.

There were quite a number of sticking points, he said, “but the main issue is that the Americans must understand that they have to recognize Iran’s rights,” including its right to peaceful nuclear enrichment under the international non-proliferation treaty.