Less than a year before London hosts the 2012 Games, scenes of rioting and looting a few miles from the main Olympic site have raised concerns about security and policing for the event.
Images of buildings and vehicles in flames broadcast around the world are also poor publicity for the capital as it prepares to stage the games for a third time.
The unrest, which started Saturday night in the Tottenham area of north London after a police shooting, spread closer to the Olympic complex Monday when scattered violence broke out in the Hackney area of east London.
''You can imagine how stretched the police would be if this were to occur during the Olympics,'' said Tony Travers, a local government expert at the London School of Economics. ''So I think this will create a worry within City Hall and the Home Office.
''It's not so much that this might happen again — unlikely — as that it reminds the people in charge that while the Olympic Games are going on, any other major event is going to be complicated.''
Groups of youths, many wearing hoods and masks, attacked shops and windows in Hackney. Police in riot gear were pelted with pieces of wood and other objects.
The government said more than 200 people had been arrested and more than two dozen charged over three days of trouble. Police said at least 35 police officers were injured.
Sports also felt the impact, with two soccer matches called off because police needed to focus its resources on the violence. East London's West Ham said police told it to postpone the League Cup match against Aldershot on Tuesday because ''all major public events in London were to be rearranged,'' while south London side Charlton said its cup match against Reading was being called off ''on safety grounds'' on advice from the police.
Hackney is one of the five boroughs encompassing the Olympic Park, a 1-square-mile site that will be the centerpiece of the games, which start on July 27, 2012. Monday's violence took place about 4 miles from the park.
The park includes the Olympic Stadium, which will host the opening and closing ceremonies and track and field competition, as well as the velodrome, aquatics center, basketball arena, handball arena and main press and broadcast center.
Other Olympic venues are located at various sites around the capital, including Hyde Park (triathlon), Horse Guards Parade (beach volleyball), Wembley Stadium (football) and Wimbledon (tennis). There has been no violence in those areas.
For civic leaders and Olympic organizers, the violence was an unwelcome reminder of London's volatility, less than two weeks after the city celebrated the one-year countdown to the games with great fanfare.
The International Olympic Committee said it had confidence in British authorities.
''Security at the Olympic Games is a top priority for the IOC,'' spokesman Mark Adams said. ''It is, however, directly handled by the local authorities, as they know best what is appropriate and proportionate. We are confident they will do a good job in this domain.''
The London organizing committee for the Olympics, declined to comment on the trouble, in what appeared to be an attempt to avoid making any links between the violence and the games.
Two police cars and a double-decker bus were set on fire Saturday, stores were looted and several buildings along Tottenham's main street — five miles from the Olympic Park — were reduced to smoldering shells.
The unrest was sparked by a police shooting, but some blamed unemployment, insensitive policing and opportunistic looting for the worst violence the city has seen in years.
Police and politicians insisted the disorder was the work of a criminal minority and not a sign of social tensions or security lapses ahead of the 2012 Games.
Britain was already preparing a massive security operation for the Olympics, but most of the attention has been on the threat of international terrorism. About 12,000 police officers will be on duty each day of the games, which have a security budget of at least $770 million.
A day after London was awarded the games in 2005, suicide bombers attacked London's transport network, killing 52 people. The British government is planning for the national terror threat to be ''severe'' during the Olympics, meaning an attempted attack is highly likely.
