Iran must prove to the rest of the world that its nuclear programme is purely for peaceful purposes, even if it agrees to a nuclear-fuel swap, top European and US officials said on Saturday.

Their comments came 12 hours after Iranian Foreign Minister Manouchehr Mottaki said that he expected a deal on the fuel swap “in the not very distant future.” German Foreign Minister Guido Westerwelle told the Munich Security Conference that such a deal “would not be a substitute ... for negotiations to ensure the civilian character of the Iranian nuclear programme.” Last year the International Atomic Energy Agency (IAEA) proposed that Iran ship low-intensity uranium abroad for enrichment, then re-import the enriched variant for use in a medical reactor, used to treat cancer patients, in Tehran.

The idea was to give Iran access to peaceful nuclear technology without it enriching uranium at home — a process world powers fear is designed to produce a nuclear bomb.

“A new country with nuclear weapons is absolutely unacceptable, be it Iran or anyone else,”Russian Foreign Minister Sergei Lavrov said.

After months of stalling, Iranian President Mahmoud Ahmadinejad on Tuesday said that his country was willing to accept the deal. On Friday, Mr. Mottaki said that that was true, but that Iran wanted to change some of the details.

On Saturday, the European Union’s new foreign-policy director, Catherine Ashton, said that she welcomed the fact that Mr. Mottaki had decided at the last minute to come to Munich.

But she stressed that the IAEA plan and overtures conducted by the US administration “have so far gone without adequate response,” warning the Iranian regime that “dialogue takes two.” US National Security Advisor James Jones also insisted that “the door for diplomacy with Iran remains open” and that Washington was ready to negotiate with Tehran.

But he also warned that US patience was not endless, saying that “Tehran’s puzzling defiance ... compels all of us to work together as allies and partners on a second track of increased pressure,” via international sanctions.

“We are doing exactly what we said we would be doing. We have not seen any indication that (Iran) is willing to do so,” Mr. Jones said.

However, sanctions would appear difficult to steer through the United Nations Security Council after veto-holder China’s foreign minister on Friday said that sanctions would be a mistake.

“In order not to complicate the situation, it is better now to concentrate on consultation and dialogue to achieve a satisfactory solution,”Yang Jiechi told the conference.

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