Iranian leaders have welcomed the offer, presented by European Union foreign policy chief Javier Solana on June 6, as a "positive step" but have rejected calls to suspend uranium enrichment on the basis of it.

Diplomats say Tehran is plainly more impressed by this offer -- drawn up by the five permament UN Security Council members plus Germany -- than a previous compromise proposal by the so-called EU-3 of France, Britain and Germany.

"Iranian leaders see this offer as fundamentally different from that of the EU-3," said an EU official, referring to the offer presented in August 2005 but immediately rejected by Tehran.

"They see it as an opportunity," added the European source.

The first part of offer is the most sensitive: in it the EU, the United States, Russia and China commit themselves to supporting the construction of light water reactors in Iran and guarantee access to fuel supplies for them.

The aim of this proposal is to persuade the Islamic republic to abandon plans to build a heavy-water reactor in Arak, central Iran, which could in theory produce plutonium usable in atomic warheads.

At the same time the West is offering guarantees to provide fuel for future nuclear power plans from outside the country -- whereas Iran wants to retain the right to enrich uranium on its own soil.

Iranian leader Ayatollah Ali Khamenei and hardline President Mahmoud Ahmadinejad have both said Tehran cannot trust the West on this score, even if they admit that Iran will have to import some nuclear fuel in the future.

On the economic front, the United States is dangling the offer of lifting an embargo on sales to Iran of commercial aircraft and spare parts, which would let the country renew its ageing and increasingly dangerous airplane fleet.

A proposal to support Iran's access to international capital markets is very important for an economy which, despite enormous oil revenues, suffers from a lack of foreign investment, new technology and from growing unemployment.

A promise to help Iran join the World Trade Organization is of less immediate interest to Tehran, since the country's economy would struggle to deal with the consquences of WTO membership.

Politically, the West's offer pledges increased efforts "to promote dialogue and cooperation on regional security issues" -- a vow certain to please Iran in terms of acknowledging its role as a key regional power.

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