Iran today gave its most negative assessment of proposals offered by six world powers aimed at persuading Tehran to give up sensitive nuclear work that the West fears is being used to make bombs.
Chief nuclear negotiator Ali Larijani said the package offered to Iran last week, which includes both incentives and penalties, contained "problems".
In previous comments, he had only referred to "ambiguities" that needed removing.
Details of the package have not been publicly announced and Iran has yet to identify specific items to which it objects, but the deal is premised on the demand Iran abandons uranium enrichment, a step Tehran has previously said was unacceptable.
Iran, the world's fourth largest oil exporter, insists it only wants to enrich uranium to low levels to make fuel for power plants. The West accuses Iran of seeking to purify uranium to the much higher levels needed to make atomic bombs. "These proposals contain some positive points.
At the same time there are problems and ambiguous points," said Mr Larijani, speaking through an Arabic translator after talks at the Arab League in Cairo. European powers - Britain, France and Germany - drew up the package that was approved by the United States, China and Russia.
It was delivered to Tehran by European Union foreign policy chief Javier Solana on Tuesday.
Some details from the proposals or early drafts have leaked from Western diplomats and other sources and they include offering Iran a light-water reactor and guaranteeing nuclear fuel supplies.
But the offer also includes possible penalties if Iran rejects it, such as imposing travel bans on Iranian individuals, freezing assets and imposing an embargo on arms sales to Iran and some Iranian exports, such as refined oil and gas products.
Mr Larijani, who heads Iran's Supreme National Security Council that has been entrusted with handling nuclear talks, said no deadline had been set for Iran to accept the package.