The presidents of Russia and the United States discussed Iran's nuclear program Tuesday before a six-nation meeting aimed at ending months of disagreement between Washington and the Kremlin and to reach a consensus on how to persuade Tehran to stop uranium enrichment.

The phone conversation between President Bush and Russia's Vladimir Putin reflected the gravity of what will be discussed at Thursday's talks in Vienna, where six countries hope to sign off on incentives and penalties designed to wean Iran off enrichment.

Tehran says it wants the technology to generate energy, but there is growing international concern it could use it to make nuclear weapons.

"Both leaders spoke in favor of the further development of international efforts in the interests of resolving the Iranian nuclear problem," the Russian government said in a statement issued after the phone call.

The European Union's top foreign policy official Javier Solana said Tuesday that Iran must prove it is not pursuing nuclear weapons and can do so by accepting the incentives that the Vienna gathering hopes finalize as part of a package meant to reward Iran if it gives up enrichment activities — or penalize it if it doesn't, possibly through Security Council sanctions.

"If they reject it, it will be once again a clear sign they are looking ... to enter nuclear weapon type of enrichment that for us will be very dangerous," Solana told the European Parliament's foreign affairs committee in Brussels.

Solana suggested that if approved in Vienna by the U.S., Russia, China, France and Britain — the five permanent Security Council members — plus Germany, the package would be formally offered Tehran before the June 21 EU-U.S. summit in the Austrian capital.

Indicating that U.S.-Russian differences remained ahead of the Vienna meeting, he said, "I hope we still have some room for maneuver."

In Malaysia, Iranian Foreign Minister Manouchehr Mottaki said his country was ready for "negotiations on Iran's nuclear issue without any preconditions."

Still, Tehran has for months insisted that its right to conduct nuclear enrichment was nonnegotiable — and nothing in Mottaki's comments suggested that stance had changed. If Iran remains defiant, the rewards component of the package up for approval in Vienna would become void and be replaced by punishment to be decided by the Security Council.

Any package foreign ministers approve on Thursday would then be presented to Tehran by France, Britain and Germany — the trio of nations that broke off talks with Iran in August after it resumed activities linked to enrichment.

The Security Council gave Iran until the end of April to suspend all such activities. Instead of complying, Iran announced last month that it had for the first time successfully enriched uranium and was doing research on advanced centrifuges to produce more of the material in less time.

Indirectly linked to any possible deal for Iran would be agreement on a resolution tough enough for Washington but acceptable to Moscow and Beijing. A dispute between the Security Council members over how to deal with Iran has hobbled action by the Security Council's permanent members for months.

If Iran remains defiant, the proposal — as outlined to AP by diplomats familiar with a draft version of the text — calls for a resolution imposing sanctions under the U.N. Charter. But it avoids any reference to an article of the charter, which can trigger possible military action to enforce any such resolution.

The proposal also calls for new consultations among the five permanent Security Council members on any further steps against Iran — a move meant to dispel complaints by the Russians and Chinese that once the screws on Iran are tightened, the council would automatically move toward military involvement.

Among the possible sanctions are a visa ban on government officials, the freezing of assets, blocking financial transactions by government figures and those involved in the country's nuclear program, an arms embargo and a blockade on the shipping of refined oil products to Iran.

If Tehran agrees to suspend enrichment, enter new negotiations on its nuclear program and lift a ban on intrusive inspections by the International Atomic Energy Agency, rewards would include agreement to "suspend discussion of Iran's file at the Security Council," as well as help in building a peaceful domestic nuclear program that uses an outside supply of enriched uranium.