Europe and the US will show a united front in condemning Iran’s nuclear ambitions when diplomats meet at a joint summit in Washington today.

But common ground will be harder to find on targets to slow down climate change, with EU diplomats privately hoping only for “continued engagement” from President Bush ahead of the G8 summit in Germany in June.

Chancellor Angela Merkel of Germany, representing the EU, and President Bush want to show that there are no cracks in their unity on Iran at a press conference tonight, following comments from Iran’s President Ahmadinejad that the EU needed to be more independent from the US.

They will also want to appear unified on their approach to Russia, which is protesting about America’s plans to host missile defence technology on Polish and Czech soil.

On climate change, Chancellor Merkel wants the next step towards a new post-Kyoto approach to global warming to be taken at the G8, which, like Tony Blair in 2005, she will chair at the same time as holding the rotating EU presidency.

These will be the main foreign affairs items on the itinerary of today's one-day EU/US summit in Washington, alongside the long-standing question of Middle East security and the crisis in Darfur.

Closer to home, the EU and US will plan cuts in red tape and harmonising economic regulations to help trans-Atlantic trade.

The American ambassador to the EU, C. Boyden Gray, has warned that the summit “will not be a defining moment” on climate change. But his negative approach annoyed some EU diplomats, who are preparing the ground for a push at the G8 once China and India, as a guest, are in attendance.

The EU has committed to a 20 per cent reduction in CO2 from 1990 levels by 2020 but the US will not take a similar step unless China and India can be persuaded to curb their own industrial emissions. Even then, the concept of a binding target to reduce CO2 is rejected by many on both sides in Washington.

The twice-yearly summit rarely provides a headline-catching breakthrough, and is even less likely to this year with big political changes due soon in France and Britain.

But Jose Manuel Barroso, the EU Commission President who will also attend the talks, has been keen to signal to Moscow and Tehran that attempts to divide the EU and the US would backfire.

In response to President Ahmadinejad, Mr Barroso told CNN that concern about Iran’s nuclear program was coming from many parts of the world, not just Washington.

“They should understand that this is not just a concern of the United States. It's a real concern of the international community,” he said. “I think the game should not be to try to divide the United States from Europe or Europe from the United States.”

Mr Barroso also said that Russia should not have a veto over US missile defence plans in Europe. “Any sovereign state of the European Union has the right to establish security arrangements with others,” he said.

His comments follow a threat by Russian President Vladimir Putin earlier this week to withdraw from a treaty that set limits on the deployment of military forces in Europe.

“We believe that the announcement to suspend Russia's participation in the Conventional Forces Treaty, that was a symbol of the Cold War, was, indeed, very disappointing,” he said.

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