Iran said on Sunday that Solana had not managed to answer all its questions on the package during a two-hour meeting with Larijani last Thursday.

The EU, which had described last week's talks as a good start, brushed off those remarks and said it still wanted a "substantive response" from Larijani on Tuesday.

"We will continue to discuss with Larijani, with the aim of getting from Iran their response to the proposals," said Solana's spokeswoman Cristina Gallach.

The talks come a day before a meeting in Paris of foreign ministers from the five permanent members of the Security Council -- the United States, Britain, France, Russia and China -- and Germany, the six powers behind the incentives offer.

The package includes a state-of-the-art nuclear reactor with a guaranteed fuel supply, economic benefits and other incentives if Iran halts uranium enrichment.

Two U.S. nuclear analysts said the offer would be more appealing to Iran if it included U.S.-backed assurances of no threats or use of force, and a pledge of quick help to restore infrastructure worn down by U.S.-driven trade restrictions.

"Iran is not prepared to relinquish (enrichment) for tenuous concessions like multilateral talks to which the U.S. is one party, or promises of nuclear and economic assistance involving long timetables and complicated conditions," said former U.N. arms inspector David Albright and analyst Jacqueline Shire.

Their Washington-based think tank Institute for Science and International Security said Iran had to be offered a way forward which "makes the decision to give up enrichment an appealing, logical step and not a humiliating, defeated one."

Iran, the world's fourth largest oil exporter, rejects charges it seeks a nuclear weapon and argues it is solely interested in electricity generation.

Oil eased on Tuesday, falling again on hopes of progress toward resolving the nuclear stand-off. London Brent was down 20 cents to $72.69 a barrel. But traders said losses were limited by Tehran's reluctance to reach an accord quickly.