Details of the basket of perks and penalties have not been made public. But an earlier draft shared in part with The Associated Press offered help in building nuclear reactors and a guaranteed supply of fuel as well as an offer to supply European Airbus aircraft for Tehran's civilian fleet.

Diplomats revealed Monday that Washington has sweetened the offer originally drawn up by France, Britain and Germany by saying it will lift some bilateral sanctions on Tehran such as a ban on Boeing passenger aircraft and related parts if Iran agrees to an enrichment freeze.

One of the diplomats also said Washington would be prepared to take some "dual-use" technology off its banned list of exports to Iran. The term is used for products and material that have military as well as civilian uses. The diplomat declined to go into details.

Solana was expected to explain the details of the package but go no further.

"This trip is not a negotiating trip. Mr. Solana is here just to present the package to Iranian officials," an official at the Supreme National Security Council told The Associated Press on condition of anonymity as he was not authorized to speak to the media.

The EU envoy, who is heading a seven-person delegation, was due to meet Mottaki before leaving Iran later Tuesday.

Iranian officials have sent conflicting signals on the initiative, reflecting a possible struggle within the leadership on how to react. Additionally, the U.S. offer to join in direct talks with Iran might have taken Tehran's top officials off guard.

Iranian President Mahmoud Ahmadinejad, normally a hardline critic of the United States who insists that Tehran has a right to enrichment, said over the weekend that a breakthrough in negotiations was possible and welcomed the U.S. offer to join talks, while rejecting preconditions.

But threats by Iran's supreme leader, Ayatollah Ali Khamenei to disrupt the world's oil supply if Tehran is punished over its nuclear program reflected Tehran's nervousness.

Although other Iranian officials have repeatedly ruled out using oil as weapon, his comments propelled oil prices to $73 a barrel Monday. Iran is the world's fourth-largest oil exporter and the second-largest producer in the Organization of Petroleum Exporting Countries.