Iranian President Hassan Rouhani expressed optimism Wednesday that a nuclear deal with world powers is imminent, saying his government is already preparing its economy for the lifting of sanctions.

"Negotiations with the P5+1 group are at a sensitive stage and the Islamic republic of Iran is preparing for (the period of) post-negotiations and post-sanctions," he said.

Rouhani made the remarks to reporters at Tehran's Mehrabad airport before flying to Russia to attend a meeting on Friday of the Shanghai Cooperation Organisation.

Iran has applied to join the SOC, which groups China, Russia and the former Soviet republics of Central Asia.

Rouhani said China and Russia are likely to hold talks on the nuclear issue at the summit in Ufa, a city about 1,100 kilometres (680 miles) east of Moscow.

The two countries form part of the P5+1 along with Britain, France and the United States plus Germany.

The Iranian president is to hold talks with his Russian counterpart Vladimir Putin on Thursday.

His assessment came as world powers readied for a late-night push to forge a deal that would curb Iran's nuclear ambitions in exchange for an easing of sanctions.

Iran and the P5+1 have effectively given themselves until Friday to reach a deal by extending a November 2013 interim accord, after missing two target dates in this round of talks now in their 12th day.

This followed what diplomats said was a stormy meeting Monday evening between US Secretary of State John Kerry and the foreign ministers of Iran and the other major powers that one senior envoy said saw a "very heated exchange of views".