Talks Wednesday between US President George W. Bush and the European Union offer the trans-Atlantic allies a new, high-profile opportunity to renew calls on Iran to abandon its nuclear ambitions.It has been tough going for the five permanent members of the UN Security Council - the United States, France, Britain, Russia and China - plus Germany to get Iran to drop the secrecy over its nuclear activities.It has been offered economic incentives in return for talks and a long-term enrichment moratorium until the international community is sure its nuclear aims are peaceful, as Tehran asserts.The negotiations with Tehran have been led by Javier Solana, the EU's foreign and security affairs chief, who has said he has had "constructive" conversations with Iran's top nuclear negotiator, Ali Larijani.Solana will attend the EU-US summit. Indicative of the sensitive nature of his dealings with Iranian leaders, a nine-page draft summit declaration contained no mention of Iran even after Bush arrived in Vienna on Tuesday evening.Speaking in Kings Point, New York, Monday, the US president said that the international community will not back down from their demand that Tehran suspend uranium enrichment."Iran's leaders have a clear choice. We hope they will accept our offer and voluntarily suspend these activities so we can work out an agreement that will bring Iran real benefits," Bush said.If Iran's leaders reject the offer of economic incentives, they will face action before the UN Security Council and progressively stronger political and economic sanctions, Bush said during a commencement speech at the US Merchant Marine Academy.Also Monday, Bush discussed Iran with Russian President Vladimir Putin in a telephone call.Iran has accused the United States of trying to sway European nations from a possible compromise. The Iranian foreign ministry said US insistence that negotiations be conditioned on Tehran's suspension of uranium enrichment has narrowed the scope of possible solutions, and made it more difficult for all parties to reach an accord.Bush made it clear he would not budge.He said allowing Iran to enrich uranium - a process that can make nuclear fuel for a power plant or fissile material for an atomic bomb - would present a grave threat to the world.