Police said they were aware that a monthly protest by cyclists was planned for Friday but ordered the protesters to remain south of the River Thames, to keep them from blocking more than 80,000 ticket-holding guests from attending the Olympics opening ceremony.
The anti-capitalist group Occupy London, part of a global movement that has waged demonstrations against financial institutions and capitalist policies, said some cyclists were members of the movement. They said police cordoned off more than 100 cyclists at one road junction near the stadium as Friday's ceremony was beginning and held them there several hours.
A Metropolitan Police statement said about 400 to 500 cyclists immediately and repeatedly sought to cross bridges north to the Olympic venue, and scores of cyclists succeeded by breaking up into smaller groups. It said police began arresting the cyclists only after several verbal warnings to leave the area were ignored.
"People have a right to protest. It is an incredibly important part of our democracy," the Metropolitan Police statement said.
"What people do not have the right to do is to hold a protest that stops other people from exercising their own rights to go about their business. That means athletes who have trained for years for their chance in a lifetime to compete; millions of ticket holders from seeing the world's greatest sporting event; and everyone else in London who wants to get around."