Mitt Romney, the Republican presidential nominee, has questioned Britain's preparedness to host the London 2012 Olympics and asked whether the country is genuinely willing to "celebrate" the Games.
Mitt Romney, who was chief executive of the Winter Olympics in Salt Lake City in 2002, spoke on the first day of a visit to Britain.
He will meet the British political leadership in London on Thursday, including David Cameron, the Prime Minister, and Nick Clegg, the Deputy Prime Minister. Mr Romney is then expected to attend the Olympics opening ceremony on Friday.
But he told US television there were "disconcerting" signs about Britain's readiness. "It's hard to know just how well it will turn out," he said. "There are a few things that were disconcerting: the stories about the private security firm not having enough people, supposed strike of the immigration and customs officials, that obviously is not something which is encouraging."
G4S, a private security company, provided thousands fewer staff than were expected, forcing the armed forces to fill the gap. British immigration officers had threatened to go on strike during the Olympics, but this ultimatum was called off on Wednesday. The Government insists that all preparations have been made and the event will be a success.
Nonetheless, Mr Romney questioned the enthusiasm of the British public. "Do they come together and celebrate the Olympic moment?" he asked. "That's something which we only find out once the Games actually begin."
However, the presidential challenger later back-tracked on the comments at a press conference on Thursday morning.
"The weather could not be better. Fortunately the sunshine is out and the warmth is here," he said. "I know the spirit and the people of this community will welcome the athletes of the world."
Asked about the mix up between Korean flags at an Olympics womens' football match in Glasgow on Wednesday night, he said it was "impossible for mistakes not to occur", adding that "of course there will be errors from time to time".
Before meeting Mr Romney, Prime Minister David Cameron said that his main priority was to ensure a safe and secure Olympic Games and that police and security services were leaving nothing to chance just a day before the opening ceremony.
"This is the biggest security operation in our peacetime history, bar none and we are leaving nothing to chance," Mr Cameron told reporters at the Olympic Park.
The comments on the Olympics came after Mr Romney's advisers told The Daily Telegraph that he would restore "Anglo-Saxon" understanding to the special relationship between the US and Britain, and return Sir Winston Churchill's bust to the White House.
"We have a very special relationship between the United States and Great Britain," Mr Romney told NBC. "It goes back to our very beginnings - cultural and historical."