LONDON, England (AFP) — US presidential hopeful Mitt Romney found himself the target of jokes in Britain yesterday, after London's mayor Boris Johnson mocked comments he made about preparations for the 2012 Olympics.

Hours after arriving for a visit designed to boost his foreign policy credentials, Romney surprised his British hosts by saying there were "disconcerting" reports about London's ability to stage the Games.

Although Romney backtracked later after talks with British Prime Minister David Cameron, his comments left a sour taste.

Addressing a crowd of 60,000 gathered in London's Hyde Park for a pre-Olympics concert, Mayor Johnson said: "There are some people who are coming from around the world who don't yet know about all the preparations we've done to get London ready in the last seven years.

"I hear there's a guy called Mitt Romney who wants to know whether we're ready. Are we ready?"

The crowd roared "yes".

Romney, who will attend the opening ceremony today, had questioned Britain's security preparations for the Games and said a now-cancelled strike by border officials was "not encouraging".

Before holding discussions with the Republican candidate, Cameron took an apparent swipe at Romney's past role as head of the 2002 Winter Olympics in Salt Lake City.

"We are holding an Olympic Games in one of the busiest, most active, bustling cities anywhere in the world," Cameron said at press conference in the Olympic Park.

"Of course it's easier if you hold an Olympic Games in the middle of nowhere."