Al-Qaeda is increasingly using online technology, including the popular social networking sites, to launch a "cyber-jihad" against the West, the British government has warned, citing terror attacks like the 26/11 Mumbai strikes.

The UK's updated counter-terrorism strategy released on Tuesday suggests that terrorists' use of social media to disseminate information and radicalise people is "commonplace".

It warns that the number of attacks on IT systems would likely increase and that extremists were increasingly sophisticated in their use of social networking and video- sharing sites.

"Since the death of Osama bin Laden, al-Qaeda has explicitly called not only for acts of lone or individual terrorism but also for 'cyber-jihad'," the document said.

"There have been a number of attempts by terrorist and extremist groups to 'invade' Facebook. Twitter will be used to re-post media or forum articles enabling extremist content to be shared more quickly, widely and amongst people who would not normally search for extremist content."

Advances in technology - such as software to encrypt mobile phone calls and texts, file sharing networks and cloud computing - meant terrorists were able to store and share material online much more easily while also disguising their actions.