Iran's President Hassan Rouhani will address the nation on state television tonight, an official statement said, amid reports a nuclear deal with world powers could be imminent.
Rouhani's appearance scheduled for 10:00 pm (1730 GMT) was announced by the culture ministry in a notice sent to media which said he would talk about the negotiations taking place in Vienna.
There had been optimism a deal would be clinched over the weekend but positive statements have been followed by talk of unresolved issues between the two sides.
Finalising a framework accord struck in April has proved difficult, with talks stumbling on the exact timing of sanctions relief and Iran's desire to have a UN conventional arms embargo lifted.
Deadlines of June 30 and July 7 have been missed but Iran and the six powers -- Britain, China, France, Russia and the United States plus Germany -- have continued to talk in the Austrian capital.
Rouhani late Sunday again raised expectations an agreement to end the 13-year dispute about Iran's nuclear programme may be resolved.
"We have come a long way. We need to reach a peak and we're very close," Rouhani said, quoted by the ISNA news agency on what was the 16th day of talks in Vienna.
"We are so close that if you look down from below you feel as if we have got there, but when you do get there you know there are still some steps to take."
Iran denies Western suspicions it is developing a nuclear bomb.
