Iran threatened to resume sensitive atomic activities unless France, Britain and Germany agreed at a meeting today to allow it to carry out small-scale uranium enrichment.
The latest proposal from Tehran suggests it be allowed to build up its uranium enrichment programme in stages, beginning with a small "pilot" enrichment plant and ending with a commercial-scale complex.
The European Union's three biggest powers are spearheading talks aimed at persuading Iran to scrap its nuclear fuel programme, fearing it could be used to build nuclear weapons, in exchange for economic and political incentives. Tehran has so far refused.
The EU powers hope to leave the hard negotiations on Tehran's atomic ambitions until after Iran's June 17 presidential elections. They view today's meeting with senior officials as little more than an informal dinner chat.
"We don't want to break things up now and have a row. We want to continue the negotiating process after the Iranian election," a European diplomat said.
But senior Iranian official Sirus Naseri, in London for the meeting, said he wanted agreement soon.
"The foundation for agreement is in place," he said. "We think it is unreasonable to avoid agreement," he added, insisting he was not putting "undue pressure" on the "EU-3".
Iran has suspended its enrichment programme under international pressure, but four months of talks with the Europeans have yielded no breakthrough and Iran says the programme must resume.
"If there is no agreement and the Europeans insist on further time ... we may have to readjust the situation so it will be a more balanced position. It will not be balanced if the suspension will remain," he added, in an apparent threat to resume enrichment unilaterally.
He later told Iran's official news agency IRNA: "in case of not reaching an agreement in London, Iran might be obliged to resume part of its uranium enrichment programme, but in that case it will still continue the talks".
Another senior nuclear negotiator said Iran would only keep talking if the Europeans said Iran's proposal was an acceptable basis for a future deal.
EU diplomats, however, said there would be no definitive response to the plan, but rather dialogue about it.