America has refused to give Iran guarantees that it will not use military force against Tehran’s nuclear sites, according to a leading official in the Bush Administration.

John Bolton, the hawkish US ambassador to the United Nations, said today that a package of incentives offered to Iran earlier this week, in return for Tehran suspending its uranium enrichment work, did not include any military commitments.

"Security guarantees are not on the table," he said in an interview during a visit to London. "Don’t even think about it."

To the dismay of America’s European allies, President Bush has insisted on keeping "all options open" in dealing with Iran, which many suspect is secretly building an atomic weapon under the guise of a civilian nuclear programme to generate electricity.

Nevertheless, there are hopes that the crisis can be resolved through diplomacy. Earlier this week Javier Solana, the European Union’s foreign policy chief, delivered a package of incentives to Tehran agreed by America, Britain, China, France, Germany and Russia.

They envisage building Iran light-water reactors, boosting trade and offering other financial inducements. The Americans have also agreed to resume official talks with Tehran for the first time in a quarter of a century.

In return Iran is expected to halt its uranium enrichment work, which many suspect is designed to produce a nuclear weapon. If it refuses, Tehran faces the threat of punitive sanctions, such as a ban on the sale of nuclear equipment and bar on travel by key figures in the regime.

Mr Bolton said that American was "being very patient", but would not wait forever for a reply. He said that Washington was expecting a response from Tehran before the middle of July when the leaders of the richest nations meet at the annual G8 summit held in St Petersburg.

"We feel that there is a sense of urgency, that these diplomatic efforts cannot go on indefinitely," he said.

Although the deal has been hailed as a breakthrough after years of stalled negotiations, Mr Bolton dismissed any notion that the resumption of direct contact between America and Iran could lead to the normalisation of full ties between the two countries.

Aside from the dispute over Iran’s nuclear ambitions, America also regards as the foremost "sponsor of terror" in the world for its support of groups like Hamas, Hezbollah and Islamic Jihad.

"It would be a mistake to think that these negotiations are a first step to some grand bargain," said Mr Bolton.

So far the leadership in Iran has sent mixed signals about how it will respond to the offer. The final decision lies with Ayatollah Ali Khamenei, but yesterday one of his key subordinates spoke out against the deal.

Ayatollah Ahmad Jannati, who heads the powerful Guardian Council, told worshippers at Friday prayers in Tehran that the offer was intended to deprive Iran of "many advantages".

"The package they have presented is a package that is good for them and not appropriate for the Iranian people," he said.

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