The government is urging people to report online terrorist content through its Directgov website.
Content so far reported through Directgov has enabled the government to remove sites which include beheading videos, terrorist training manuals and calls for racial or religious violence, it said.
"In this digital age it is vital that the threat of online extremism and the increase in terrorist content on the internet is taken very seriously. I would urge anyone who may come across extremist websites and content to take action and report it through the Directgov webpage or directly to the administrator or hosting company," said Baroness Neville-Jones, Security Minister.
Jayne Snelgrove, head of the Counter Terrorism Internet Referral Unit, said: "Policing within the environment of the internet is a relatively new area but we are aiming to make it a more hostile place for people who use it for criminal purposes. The Counter Terrorism Internet Referral Unit is focused on material which is used for terrorist purposes or to promote extremist messages that radicalise vulnerable people.
"A lot of what is referred to us by the public may not breach the law; however, we are best placed to conduct that assessment and it's important that we know the scale and range of material available to the public."
The government has so far used the Directgov site to enable the:
Removal of terrorism related videos encouraging martyrdom operations and associated postings that had been uploaded to a UK based website
Shutting down a website that provided detailed video instructions into bomb making
A number of videos which encouraged acts of terrorism were removed from a social networking site
Removal of a number of videos that were encouraging support for a proscribed terrorist organisation were removed from a social networking site
Jayne Snelgrove, detective chief inspector, discussing the importance of the Directgov site in countering terrorism
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