Iranian and American officials were deadlocked yesterday after their most highly publicised meeting for nearly 30 years failed to produce a breakthrough on Iran’s nuclear enrichment programme.

After six unproductive hours the Iranians were given two weeks to respond.

“Iran has a choice to make: negotiation or further isolation,” said US State Department spokesman Sean McCormack.

The negotiations, in Geneva, allowed the United States to press its demand for the immediate suspension of Iran’s uranium enrichment programme, which many in the West suspect is designed to develop nuclear weapons.

However, Iran refused to agree to any such proposal despite signs before the talks that it might be prepared to suspend nuclear activities in exchange for a package of economic incentives.

The meeting was hosted by Javier Solana, the European Union’s diplomatic chief, and attended by the five permanent members of the United Nations security council (the United States, Russia, China, France and Britain) and Germany.

Diplomats described the talks as a final attempt to persuade Iran that it must freeze its nuclear programme.

“They can take this message away with them to Iran,” said a British official. “If they don’t agree to our proposals, we will have to start imposing sanctions.”

By attending the talks William Burns, the American undersecretary of state, ended the diplomatic boycott of Tehran by the United States over the issue.

Iran was urged to agree to a “freeze for freeze” proposal that would require it to suspend all progress on nuclear enrichment for six weeks.

In return, no new sanctions would be imposed for the same period and formal negotiations to end the long-running dispute could begin.

Iran has been offered a wide-ranging package of incentives including investment in education, infrastructure, aviation, development and science, if it halts its nuclear programme.

There are fears that if Iran presses ahead Israel will launch an attack on the nuclear facilities, sparking another Middle Eastern conflict.

Before travelling to Geneva, Saeed Jalili, Iran’s top nuclear negotiator, said he hoped the talks would be “constructive”.

Yesterday the Iranians sounded more pessimistic. “Any kind of suspension or freeze is out of the question,” said Keyvan Imani, Iran’s ambassador to Switzerland.

Condoleezza Rice, the American secretary of state, said the decision to send Burns showed that Washington was determined to pursue diplomatic efforts.

“It is, in fact, a strong signal to the entire world that we have been very serious about this diplomacy and we will remain very serious about this diplomacy,” she said.

David Miliband, the foreign secretary, said: “It is the moment of choice for the Iranians. I strongly welcome the decision by the US to send Bill Burns to the meeting.”

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