The main Olympics site in east London was one of the targets of rioters, but an attack there was prevented after the police picked up intelligence on social networking sites.

Assistant commissioner of police Lynne Owens told the Home Affairs Committee on Tuesday that the police prevented attacks by rioters on the Olympic site and London's Oxford Street after picking up intelligence on social networks.

Riots and looting was reported from Hackney, one of the five boroughs in which the 2012 London Olympics will be held. Information about possible attacks was picked up via Twitter and BlackBerry messenger, he said, while Acting Commissioner Tim Godwin said he had considered asking authorities to switch off social networks.

Keith Vaz, chairman of the committee, said the information about social networking sites given by the police officers was most interesting.

Much of the looting and rioting was allegedly coordinated via social media, particularly through BlackBerry Messenger service, leading to demands that police have powers to shut them down during crisis.

Owens told the committee: "Through Twitter and BBM there was intelligence that the Olympic site, that both Westfields [shopping centres] and Oxford Street were indeed going to be targeted". She added: "We were able to secure all those places and indeed there was no damage at any of them."

Godwin said the police considered trying to shut the networks down in order to prevent them being used to organise further violence. He said: "We did contemplate, I contemplated, asking the authorities to switch it off. The legality of that is very questionable and additionally, it is also a very useful intelligence asset".

BlackBerry has offered to co-operate with police investigating the riots - prompting attacks by hackers angry that the company could be prepared to hand over user data to authorities.

British intelligence agency MI5 has now been asked to contribute to efforts to decode traffic through the social media during the riots.