The two sides are to meet again in Vienna tomorrow to try to build on an interim agreement reached late last year in Geneva by reaching a final settlement of the decade-old dispute over the Islamic Republic's atomic activities by late July.
"This round of negotiations compared to the previous ones will be more serious and tougher," Foreign Minister Mohammed Javad Zarif told a news conference. "We do not expect to come to an agreement."
None was expected so soon in the new round of negotiations, Western diplomats said earlier. The six powers and Iran have set a deadline of late July to reach a long-term agreement.
Most of Iran's 290 parliamentarians came out strongly yesterday against putting any limits on the Arak heavy water reactor, which remains under construction.