LONDON -- Violence and looting spread across some of London's most impoverished neighborhoods yesterday, with youths setting fire to shops and vehicles, during a third day of rioting in the city that will host next summer's Olympic Games.

Skirmishes broke out between police and groups of youths across Britain's capital, and also spread to the central city of Birmingham -- where police said dozens of people were involved in damaging shops across the city center.

In the Hackney area of east London and districts in the city's south, vehicles and buildings were set ablaze as authorities struggled to halt groups of rampaging young people.

Hundreds of youths attacked shops and set fire to cars in Hackney, while police in riot gear were pelted with fireworks, bottles and lumps of wood.

Thick smoke billowed from a high street in the Peckham district of south London, where a building was set ablaze along with a bus -- which was not carrying passengers. In nearby Lewisham, lines of cars were torched.

Police confirmed they had made more than 200 arrests.

Prime Minister David Cameron announced he would cut short his summer vacation in Italy and will convene a meeting of the government's crisis committee Tuesday.

Despite the arrests and the deployment of hundreds of reinforcements, police appeared unable to contain the spread of the rioting, which began Saturday night amid community anger over a fatal police shooting.

Mark Duggan, 29, a father of four, was gunned down in disputed circumstances Thursday in the Tottenham area of north London.

Though the initial unrest was sparked by Duggan's shooting, 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.

In the hardest-hit area, Tottenham, many residents agreed that the looting was the work of greedy youths, aided by instant communication through texts and instant messaging.

"It's nothing to do with the man who was shot, is it?" said Marcia Simmons, 37, who has lived in the diverse and gritty north London neighborhood all her life.

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