Iranian and Russian officials said in June the long-delayed start-up at the Bushehr plant had been set for sometime in August but that timetable was thrown into question by comments last week by Russian Foreign Ministry spokesman Alexander Lukashevich.
Lukashevich told Russian television there was no "specific date" for firing up the plant, which Russia has been helping Tehran to build since 1995.
And that prompted a warning Saturday from Hossein Ebrahimi, the deputy chairman of the Iranian Parliament's National Security and Foreign Policy Commission, who said Iran won't tolerate any more delays from Moscow, Fars News Agency reported.
The Russian state nuclear power corporation Rosatom is legally obliged to supply Iran a specific start-up date, he added.
"According to the contract, the Russian company is bound to fulfill its undertakings with respect to the completion and launch of the plant," Ebrahimi said.
"The Islamic Republic will no longer accept any ambiguity or justification (for delays) with regard to the launch of the Bushehr nuclear plant, and nuclear-generated electricity should enter the grid at the specified time."
The start-up of the German-designed, 1,000-megawatt Bushehr plant was originally set for 1999, four years after Russia struck a deal with Tehran to complete it. But Moscow, under pressure from the United States and its allies, has delayed its completion since then.
U.S. officials fear that low-enriched nuclear fuel rods from the light-water atomic reactor could be diverted into stock for a potential nuclear weapon, while Tehran insists it seeks only produce electricity.
Russia finally completed construction of the plant last year under the supervision of the International Atomic Energy Agency and Iran has publicized plans for a large-scale celebration to mark the opening of Bushehr, four decades after it was begun under the reign of Shah Mohammad Reza Pahlavi in the mid-1970s.
But Lukashevich's comments seemed to cast doubt on the plant's timetable and indicated Russia is seeking a signal from Tehran.
The energy industry trade Web site OilPrice.com reported the Russian spokesman told Rossiya 24 television Moscow is waiting for Iran to express a "preference."
"Deputy Foreign Minister Alexei Borodavkin, talking to journalists, I believe, described the situation by saying that we would very much like to receive a more precise expression of preference from our Iranian colleagues: When is it convenient to them for the facility to be launched?" Lukashevich said.
Iranian Foreign Minister Ali Akbar Salehi said in June Tehran was preparing a late August official launch and start-up of power generation.
"The reactor will reach 40 percent of its power capacity in the middle of the holy month of Ramadan (mid-August) and (it) will join the national grid later in the month," Salehi said in a June 28 interview with Iran's state-run television service.