By Christopher Adams in London and Guy Dinmore in Washington
Britain will on Monday seek to narrow differences between Europe and the US over Iran's nuclear programme, with Jack Straw, foreign secretary, expected to urge Washington to take a positive approach to talks with the Islamic republic.
Mr Straw is expected to meet Condoleezza Rice, incoming US secretary of state, for the first time since her appointment to replace Colin Powell. The British foreign secretary enjoyed a close relationship with Mr Powell and will be seeking to establish a similar rapport with his successor.
The talks will take place amid a flurry of diplomatic activity in Washington. They will give London its first real opportunity since the re-election of George W. Bush to test the US president's resolve to pursue what Tony Blair has predicted will be a more consensual foreign policy.
High on the agenda will be the future course of negotiations led by the UK, France and Germany with Tehran over its suspected nuclear facilities, following an agreement that it will suspend uranium enrichment.
Concern is growing in some western capitals that a sceptical Bush administration is preparing to adopt a tougher approach towards Iran. Diplomats want to see clarification of remarks by Vice-President Dick Cheney, who said Iran was right at the top of the list of potential troublespots.
Mr Cheney said last week the US wanted a diplomatic solution, but the Israelis might well decide to act first and let the rest of the world worry about cleaning up the diplomatic mess afterwards.
Mr Straw will use the talks to try to influence the formulation of US policy. He is expected to concentrate on how Tehran can be persuaded to abandon its nuclear programme and agree to a set of objective guarantees that it will not build a weapon, in return for access to world markets.
At the same time, officials from the three European countries negotiating with Iran will meet Stephen Hadley, designated the next US national security adviser. Germany's foreign minister, Joschka Fischer, is expected to meet Ms Rice tomorrow.
In London on Sunday senior British officials played down the possibility of a military strike against Iran.
One official, while conceding there were differences between Washington and London, said he was not aware of any serious political consideration being given to military action: In present circumstances it would be hard to see how that would be justified.
But there was also a recognition that no American president was going to rule out the use of force as an option.
The official said: They [the US"> recognise that the agreements and dialogue over the last 18 months have produced some important steps. Equally, the Americans are sceptical about Iranian intentions. . . we share their concerns.
In Tehran, Iranian officials struck a defiant stance, describing Mr Cheney's remarks as psychological warfare and saying any attack would be a major strategic mistake.
Mr Straw and Ms Rice are also expected to discuss US concerns about the prospect of an end to the EU arms embargo on China.