G8 foreign ministers meeting in Moscow said they were disappointed Iran had yet to respond to the offer.
The ministers want Iran to give its reply at a meeting next week with EU foreign policy chief Javier Solana.
But Iran, which denies seeking nuclear weapons, restated on Thursday it would respond to the offer in August.
Foreign Minister Manouchehr Mottaki said his nation was considering the incentives package presented earlier this month.
“The Islamic Republic of Iran is seriously and carefully reviewing the proposed package,” he said.
EU talks
A ministerial statement said the G8 expected a response to the proposals by 5 July when Mr Solana will hold talks with Iran’s top nuclear negotiator, Ali Larijani.
“We are disappointed in the absence of an official Iranian response to this positive proposal,” it said.
“An agreement of this sort would allow the Iranian people to enjoy the benefits of modern civil nuclear power and would bring Iran many other long-term political and economic advantages.”
The ministers were meeting in Moscow ahead of a summit of G8 leaders in mid-July in St Petersburg.
The six major nations involved in negotiating with Tehran – the United States, Britain, France, China, Russia and Germany – will assess the situation just before the summit.
Iran says its programme is entirely peaceful and is designed to meet its energy needs, but the US and other powers say it is using it to develop nuclear weapons.
