Mitt Romney has questioned London's readiness to hold the Olympic Games as he toured the capital, saying the fiasco over security arrangements and a planned strike by UK border staff were "disconcerting".
"You know it's hard to know just how well it will turn out," the Republican presidential candidate told NBC News on Wednesday. "There were a few things that were disconcerting."
"The story about the private security firm not having enough people, the supposed strike of the imigration and customs officials, that is not something that is encouraging."
Romney, who ran the 2002 Winter Games in Salt Lake City, said there were "three parts" to ensuring the Olympics were a success.
"Number one is the athletes," he said. "Number two is the volunteers, they'll have great volunteers here."
"Number three, are the people of the country, do they come together and celebrate the Olympic moment? That is something we only find out once the Games actually begin."
Romney also responded to questions over the mix up with North Korea's flag at a football match on Wednesday, saying: "It is impossible for absolutely no mistakes to occur.
"Of course there will be errors from time to time, but those are all overshadowed by the extraordinary demonstrations of courage, character and determination by the athletes.
His comments came during a visit to London where he is meeting David Cameron, Ed Miliband and Nick Clegg. After staying in the city to watch the Olympic opening ceremony he will fly on to Poland and Israel.
Romney's wife Ann also has an interest in the London Games, as she has a horse competing in the equestrian events.
While Romney wished his wife's horse well, he said he would not be paying too much attention.
"I have to tell you this is Ann's sport, I am not senve sure what day the sport goes on, she will get a chance to see it, I will not be watching the event."
Rafalca, the horse, is due to make an appearance in the dressage on 2 August