Social media sites have been criticised over the speed of their action to remove footage of the New Zealand mosque shootings.
Labour’s shadow digital secretary Tom Watson said Google’s response was “not good enough” after YouTube “reviewed” the video before removing it from the site.
Damian Collins, the Tory chairman of the Digital, Culture, Media and Sport Select Committee, called for a review into how the films were shared and “why more effective action wasn’t taken to remove them”.
And Downing Street said social media companies need to act “more quickly” to remove terrorist content.
Suspect – Brenton Tarrant – appeared to have livestreamed the attack on Facebook as victims in a mosque were shot.
Mr Collins criticised social platforms including Twitter, Reddit, Google and Facebook for allowing users to find and re-post the footage.
He told the Press Association: “These platforms are being used to disseminate the vilest content and make people aware of its existence.
“We should look at companies like that and say for them to allow their platforms to be used in that way is damaging to society. It’s hugely harmful.”
He called for a regulator to have the power to sanction companies allowing the spread of “harmful content”, adding that the “ultimate sanction” would be to bar them from the internet.
Facebook said it “quickly removed” the video, while YouTube said it was “working vigilantly to remove any violent footage”.
Mr Watson hit out at Google for not taking the video down from YouTube immediately.
He said: “Google have contacted me to explain that they posted the “inappropriate” content warning on the NZ massacre footage while they “reviewed the video” for YouTube.
“Not good enough. They should have just taken it down, then reviewed it.”
Mr Collins added that it was “very distressing” that the attack was live streamed on social media and that “footage was available hours later”.
“There must be a serious review of how these films were shared and why more effective action wasn’t taken to remove them,” he added.
Facebook New Zealand’s director of policy Mia Garlick said in a statement: “Our hearts go out to the victims, their families and the community affected by this horrendous act.
“New Zealand Police alerted us to a video on Facebook shortly after the livestream commenced and we quickly removed both the shooter’s Facebook and Instagram accounts and the video.
“We’re also removing any praise or support for the crime and the shooter or shooters as soon as we’re aware.
“We will continue working directly with New Zealand Police as their response and investigation continues.”
YouTube said on Twitter: “Our hearts are broken over today’s terrible tragedy in New Zealand.
“Please know we are working vigilantly to remove any violent footage.”
A Twitter spokeswoman said: “We are deeply saddened by the shootings in Christchurch today.
“Twitter has rigorous processes and a dedicated team in place for managing exigent and emergency situations such as this.
“We also co-operate with law enforcement to facilitate their investigations as required.”
A Downing Street spokeswoman said: “They have taken action to take it down and we are clear that all companies need to act more quickly to remove terrorist content.
“There should be no safe spaces for terrorists to promote and share their extreme views.”