The British government has said it wants to combat Islamic extremism on the internet in the same way it fights material depicting child sexual abuse.
British Home Secretary Jacqui Smith, in her first major speech on countering Islamists, drew an analogy between the militant recruitment of impressionable youngsters on the internet and the online stalking of children by paedophiles.
She told a security conference that the internet is not a no-go area for government.
Ms Smith said she planned to consult with the internet industry in the coming weeks and she wants to develop filters to remove militant material from the web like those commonly used to stop children accessing adult content.
Many internet users are sceptical about the feasibility of closing down militant web sites, which may be hosted anywhere in the world, or blocking access to them.
When sites are shut, the same material often pops up instantly elsewhere.
The European Commission last year floated the idea of trying to block web searches for material such as bomb-making recipes and obliging Internet Service Providers to prevent access to sites containing them, but later backed away from such censorship.
ISPs already cooperate with police to shut down sites that are clearly illegal, such as those dealing in child pornography.
But they say combating militants involves issues of free speech and subtle distinctions between material that is illegal and content that is merely objectionable.
They say it is not their job to police billions of web pages and so the onus is on the authorities to bring criminal content to their attention.
