EU foreign policy chief Javier Solana presented a package of incentives for Iran, which many countries suspect of pursuing a secret weapons program, in return for its consent to halt uranium enrichment during his visit to the Islamic Republic on June 6.
Solana is currently discussing the incentives with Iran's top nuclear negotiator, Ali Larijani, in Brussels.
Spokesman Hamid Reza Asefi said Iran's experts were uncertain about "the political and economic blocs and details with regard to civilian nuclear power."
He said Europe should clarify these points as soon as possible so that Iran could give a final answer to the proposals.
The five permanent UN Security Council members and Germany, who drew up the proposals, want Iran to respond before the next summit of the Group of Eight industrialized nations on July 15-17.
Larijani earlier said his country would give response in August.