For months, Britain, France and Germany have hoped to improve their bargaining power with the Islamic republic by involving Washington in a proposed accord over an end to its uranium enrichment activities.
That effort has intensified since President George Bush's re-election in November, culminating with ministerial visits to Condoleezza Rice days before she took up her new post as secretary of state, they said.
So far, the Americans show no sign of giving ground.
"It's what they [the Europeans] have always wanted to do," a senior Bush administration official said, adding that British Foreign Secretary Jack Straw "came over hoping Condi would change our policy and she didn't".
A senior State Department official said Straw, who visited
before Germany's Foreign Minister Joschka Fischer went on a similar mission, outlined European hopes for the negotiations.
The idea of getting the Bush administration into the talks
"is in the air", he said.
"But we have not been [formally] asked yet and when we are,
we will say: 'What good would it do?'"
The US takes a harder line than the Europeans and wants Iran, which Bush has grouped in an "axis of evil" with pre-invasion Iraq and North Korea, to be reported to the UN Security Council for possible international sanctions.
US officials say that would increase pressure on Iran and
push council members China and Russia to curtail arms and
energy deals with it, respectively, which Washington thinks could boost Iran's nuclear capability.
Power for people
Iran denies US accusations it is pursuing a nuclear bomb and says its programmes are only for peaceful power generation needed to keep up with its growing population.
A European diplomat acknowledged the lobbying had failed to
overcome US scepticism about the talks, but Europe hoped
Washington would be persuaded if Iran kept to the agreement that offers energy, technology and trade incentives.
"The Europeans believe that the US position will evolve in accordance with how Iran lives up to its commitments.
"But frankly there remains scepticism within the administration as to whether Iran is willing or capable of the transformation required," the diplomat said.
Urged to participate
The Europeans - with reluctant US acquiescence - have negotiated a freeze on Iran's uranium enrichment in an accord
similar to one that broke down last year.
Enrichment, which Iran has refused to give up permanently, can help generate power or make bombs.
The head of the UN nuclear agency on Friday urged the US to join the talks.
On Sunday, Rice told the US TV programme Face the Nation: "We really do believe ... that this is something that can be dealt with diplomatically. What is needed is unity of purpose, unity of message to the Iranians, that we will not allow them to skirt their international obligations and develop nuclear weapons under cover of civilian nuclear power."
Her remarks came after the president refused to rule out a
military strike and his vice-president said Iran was at the top of the world's trouble spots and warned the region's biggest US ally, Israel, could hit its facilities.
Visit to Gulf
A senior US official said on Monday that he was consulting with Gulf Arab states to coordinate policies in light of the perceived Iranian threat.
John Bolton, the State Department's top international security official, said he has explained to Gulf leaders the American view on the "Iranian problem and how we've been dealing in the past and how we proposed to deal with in the future".
Bolton, who arrived in Bahrain from Kuwait, is also visiting the United Arab Emirates on his tour of US-friendly Gulf countries.
"There are a series of things that we have discussed in which additional diplomatic pressure can be put on Iran to prevent them from acquiring the necessary material and technology that they need for their nuclear weapons programme," he said.