Barack Obama declared yesterday that he would shift “the central front in the War on Terror” from Iraq to Afghanistan, promising a “new era of international co-operation” in which America would once more lead — rather than alienate — the rest of the world.

He condemned President Bush’s “single-minded and open-ended focus on Iraq”, saying that it had diverted resources from what should have been the top priority of Afghanistan — “a war that we have to win” — where he promised to send at least two more combat battalions.

The Democratic candidate delivered his key speech on foreign policy in Washington before a trip to Europe and the Middle East next week when his credentials as a potential commander-in-chief are expected to come under intense scrutiny.

Although he insisted that his plan to withdraw combat brigades from Iraq within 16 months was possible, Mr Obama was careful to say that he would make “tactical adjustments” according to advice from military commanders and that an unspecified “residual force” would remain.

John McCain, his Republican rival, was scornful, pointing out that Mr Obama had chosen to set out plans without witnessing recent progress in Iraq or even setting foot in Afghanistan. “In my experience,” he said, “fact-finding missions usually work best the other way around: first you assess the facts on the ground, then you present a new strategy.”

The precise itinerary of Mr Obama’s trip is being kept opaque for security reasons but it is understood that he has changed plans to start his overseas tour in Britain and will now visit the Middle East before travelling to Europe.

One highlight is expected to be a rally in Berlin, a city rebuilt after the Second World War with US help that Mr Obama described yesterday as symbolising his country’s capacity to “shape events not just through military force but through the force of our ideas”.

He added: “It’s time for America and Europe to renew our common commitment to face down the threats of the 21st century just as we did the challenges of the 20th.”

There are, however, nuanced disagreements emerging between Mr Obama and European governments on his foreign policy. During a trip to Washington last week, Des Browne, the Defence Secretary, made plain his distaste for withdrawal timetables from Iraq, saying that they do “not serve any of us”.

Mr Browne also gave warning that it was impossible to seal the border between Afghanistan and Pakistan, pointing out that the British military had never managed to do so in the far less hostile terrain of Northern Ireland. Like other Nato members in Afghanistan, Britain places less emphasis on a purely military solution.

Mr Obama said yesterday that he wanted to secure the border, adding: “We need more troops, more helicopters, more satellites, more Predator drones.” He reiterated that the US forces should be ready to cross into Pakistan without permission “to take out high-level terrorist targets like bin Laden if we have them in our sights”.

Germany is among the Nato members who are feeling pressure from Mr Obama to remove caveats limiting the role of its troops in Afghanistan to non-combat operations.

His promise to hold direct talks “without preconditions” over Iran’s nuclear ambitions has raised eyebrows in Europe, where business has paid a high price for a united front from the West.

Yesterday Mr Obama was careful to “commend the work of our European allies on this important matter” and promised that there would be careful preparations before any meeting with the Iranian leadership. He pledged to “use all elements of American power to pressure the Iranian regime”.

Much of the speech was pitched towards American voters. According to an opinion poll published yesterday, fewer than half say that Mr Obama would be a good commander-in-chief, compared with 72 per cent for Mr McCain.

Mr Obama said that neither President Bush nor Mr McCain had “a strategy for success in Iraq – they have a strategy for staying in Iraq”. He added: “At some point, a judgment must be made. Iraq is not going to be a perfect place and we don’t have unlimited resources to try to make it one.”

Mr McCain said that his opponent had been proved wrong when he predicted that the military surge in Iraq 18 months ago would increase sectarian violence. “I know how to win wars,” he said.

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