The US ambassador will tell Muslims in Birmingham today that his country cannot wave a magic wand in Iraq and make its complex problems go away.
Ambassador Robert Holmes said while there might be a political cost for parties which supported the war, it was a crucial part of the war on terror.
He was speaking on the first of a two-day tour to the city, during which he is meeting America's business partners from the region and also visiting Birmingham Central Mosque and Birmingham University.
Last night he was guest of honour at a dinner held at the Colmore Row offices of Wragge & Co, which was organised by the British American Business Council for the Midlands.
Ambassador Holmes said he was expecting some "tough questions"
during his visit about the war in Iraq, but said he hoped to win some friends for the US.
"The war is not only controversial in the UK but the US," he said. "Both the President and the Prime Minister have taken tough decisions."
He went on to justify the troops' continuing presence in Iraq.
"Three times last year the Iraqis went to the polls and each time more people turned out than to the previous election," he said. "I think the Iraqis would like a fresh chance to have a democratic society. In spite of the insurgency it seems clear the majority of the people want to live in freedom.
"Sometimes there's a belief that the US can just wave a magic wand and solve every problem. Sometimes that's just not possible and it takes time and diplomacy."