Deputy Foreign Minister Mhedi Mostafavi made that prediction as the six major UN powers are considering a draft resolution offered by Britain, France and Germany in consultations with Washington.
It calls on UN member states to slap nuclear and ballistic missile-related sanctions on Iran. It provides for a freeze of assets related to Iran's nuclear and missile programs and travel bans on scientists involved in those programs.
But Mostafavi, quoted by state news agency IRNA, said "not only will this draft not be adopted, but even a much weaker one would only be (adopted) with great difficulty."
He did not give any reasons for his confidence, but permanent UN Security Council members Russia and China have repeatedly signalled their reluctance to accept biting sanctions against Iran, a major energy and trade partner.
Envoys from the Council's five veto-wielding members -- Britain, China, France, Russia and the United States -- plus Germany held a first private meeting on Thursday on the draft resolution. They are expected to resume discussions later this week.
Iranian President Mahmoud Ahmadinejad warned on Monday that Iran would react firmly to any UN sanctions imposed on Tehran.
"We are not looking for tension but any action that aims to limit us will receive an appropriate and firm response from the Iranian people," he said.
On Saturday, Tehran confirmed that it had successfully enriched uranium from a new cascade at a nuclear plant, hailing the move as a step towards industrial-scale enrichment.
Enrichment, carried out in lines of centrifuges called cascades, is used to make fuel for civilian nuclear reactors. In highly refined form, however, the product can also serve as the raw material for atomic weapons.
Western countries suspect that Iran's enrichment program is designed to supply material for a nuclear weapon, while Tehran insists its fuel processing is for peaceful purposes.

Copyright AFP (Agence France-Presse), 2006