While Iranian President Hassan Rouhani said an agreement was close, US Secretary of State John Kerry noted that both the parties did not agree on several points either.
The US along with UK, France, Russia, China and Germany, jointly known as (P5+1), have been holding negotiations with Iran to finalise a preliminary agreement, which was agreed in 2013 in Geneva.
While the P5+1 want Iran to restrict its nuclear program, Iran says that its program is focused at building atomic energy and not on nuclear weapons.
The countries have agreed to extend the discussions and aim to arrive at a political agreement by 1 March 2015. They aim to confirm the complete technical details of the deal by 1 July 2015.
During this period, Iran will be able to access $700m every month in frozen assets, reports BBC.
In an interview that was broadcast on state television, the Iranian President remarked that during the latest round of negotiations in Austria, the gap between the two sides had significantly "narrowed".
"It is true that we could not reach an agreement but we can still say that big steps have been taken," Rouhani added.
Taking a more cautious approach, Kerry noted that the talks indicated a "substantial progress" but some points of disagreement still need to be sorted out.
"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," Kerry told reporters.
