American intelligence agency FBI is reportedly developing new software to scan social networks Twitter and Facebook to look for emerging threats and predict crimes.

The FBI has asked technology firms to create software that can effectively scan the websites for words, phrases and other suspected behaviour, the Telegraph reported.

It will also be able to translate from foreign languages as well as detect patterns of users misleading the police.

Campaigners of free speech have now raised concerns.

Jennifer Lynch, from the Electronic Frontier Foundation, said it could erode the sense of freedom provided by the internet.

"These tools that mine open source data, and presumably store it for a very long time, do away with that kind of privacy. I worry about the effect of that on free speech in the US," she said.

Privacy International said the move risked placing large numbers of people under surveillance.

Police in Britain already use Facebook routinely to ascertain the whereabouts of criminals.