"I don't think that... we will reach a deal, so we'll take the third step and we will announce the details today or tomorrow," Rouhani was quoted as saying on Wednesday by the presidency website.

Iran and three European countries -- Britain, France and Germany -- have been engaged in talks to save a landmark 2011 agreement that has been unravelling since the US withdrew from it in May last year.

The efforts have been led by French President Emmanuel Macron, who has been trying to convince the US to offer Iran some sort of relief from sanctions it has reimposed since its pullout.

In his remarks on Wednesday, Rouhani said the two sides were getting closer to an agreement on a way to resolve burning issues.

"If we had 20 issues of disagreement with the Europeans in the past, today there are three issues," the Iranian president said.

"Most of them have been resolved but we haven't reached a final agreement."

The 2015 nuclear deal was agreed between Iran and the so-called 5+1 -- UN Security Council permanent members Britain, China, France, Russia and the United States plus Germany.