Social media companies are “consciously failing” to combat groups using their services to promote extremism, say MPs.
The Home Affairs Select Committee said firms including Facebook, Twitter and Google, which owns YouTube, must show “a greater sense of responsibility”.
The three companies have each said they take their role in combating extremism and terrorism very seriously.
Industry body techUK said the MPs had painted “an inaccurate picture” of how much work was being done.
In its report, the committee accuses the companies of “passing the buck” over combating online extremism – although one expert said the conclusions were arguably simplistic and misleading.
The MPs said: “Networks like Facebook, Twitter and YouTube are the vehicle of choice in spreading propaganda and they have become the recruiting platforms for terrorism.
“They must accept that the hundreds of millions in revenues generated from billions of people using their products needs to be accompanied by a greater sense of responsibility and ownership for the impact that extremist material on their sites is having.”
Keith Vaz, chairman of the committee, accused the networks of “hiding behind” their supranational legal status and said they should publish more details about how much material they are removing – and how quickly they do so.
A Scotland Yard unit that works with social media companies is currently overseeing the removal of more than 1,000 pieces of extremist or illegal material a week – although the companies do not always agree to requests.
During the recent trial of radical cleric Anjem Choudary for inviting support for so-called Islamic State, it emerged that police had asked social media companies to remove some content or accounts linked to him and his co-accused, but not all of the requests were acted upon.
Twitter has declined to comment directly on the committee’s conclusions, but told the BBC it has shut down more than 360,000 extremist accounts since last summer.
Just last week the US State Department – which is among a network of government organisations that has been working with social media companies to combat online extremism – praised Twitter’s efforts – as has France’s interior minister.
Simon Milner, director of policy for Facebook UK, told the BBC the company had given extensive evidence to MPs about how it had been developing its counter-extremism strategy.
“Terrorists and the support of terrorist activity are not allowed on Facebook and we deal swiftly and robustly with reports of terrorism-related content,” said Mr Milner.
“In the rare instances that we identify accounts or material as terrorist, we’ll also look for and remove relevant associated accounts and content.”
And a spokesman for YouTube said: “We take our role in combating the spread of extremist material very seriously. We remove content that incites violence, terminate accounts run by terrorist organisations, and respond to legal requests to remove content that breaks UK law.
“We’ll continue to work with government and law enforcement authorities to explore what more can be done to tackle radicalisation.”
The report criticised the companies for failing to be more specific about some of their efforts, including how many staff they had working on counter-extremism, and whether they had devoted sufficient resources from their vast revenues to developing systems that could automatically identify and remove content.
But technology and terrorism experts have challenged the conclusions.
“Social media companies are doing a lot more now than they used to – no doubt because of public pressure,” said Prof Peter Neumann, from Kings College London, an expert on radicalisation.
“That said, the vast majority of ISIS recruits that have gone to Syria from Britain and other European countries have been recruited via peer to peer interaction, not through the internet alone.
“Blaming Facebook, Google or Twitter for this phenomenon is quite simplistic, and I’d even say misleading.”
And Charlotte Holloway, of techUK, said combating extremism was “a serious and ongoing priority” for the firms, “backed by significant resources, a zero-tolerance approach, and decisive and fast action when needed”.
“Tech companies work proactively to deal with online extremism daily, in constructive and proven partnerships with a wide range of policy-makers, the police and security agencies, and wider civil society bodies,” she continued.
“Indeed, the vast majority of counter-terrorist operations would not succeed without the assistance and support of tech companies.”
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