25/11/2014 10:44
John Kerry said there are still some "significant points of disagreement"
Speaking in Tehran on Monday evening, President Rouhani said the gap between the two sides had "narrowed" during the latest round of talks in Vienna.
"It is true that we could not reach an agreement but we can still say that big steps have been taken," he said in an interview broadcast on state television.
Mr Kerry was more cautious, warning that although "substantial progress" had been made there are still "some significant points of disagreement."
"These talks are not going to get easier just because we extend them. They're tough. They've been tough. And they're going to stay tough," he told reporters in Austria's capital.