Social media sites have become "the command-and-control networks of choice for terrorists", a senior British spy said Tuesday, warning that some US technology companies are "in denial" over the issue.
Robert Hannigan, the new head of electronic spying agency GCHQ, used a Financial Times article to urge Silicon Valley big names to give security services more help in the fight against Islamic State (IS) jihadists.
The rare public comments by a senior intelligence officer will fuel the debate ignited by US leaker Edward Snowden over how much access governments should have to personal online information and what steps social networks should take to regulate content.
Classified information released by former intelligence analyst Snowden in 2013 revealed that GCHQ played a key role in covert US surveillance operations worldwide, including monitoring huge volumes of online and phone activity worldwide.
While Hannigan did not name firms directly, he highlighted militants' use of Twitter, Facebook and WhatsApp and referred to graphic online videos showing the final moments of Western hostages executed by the IS group.
"However much they dislike it, they have become the command-and-control networks of choice for terrorists and criminals," he wrote in the FT.
"To those of us who have to tackle the depressing end of human behaviour on the Internet, it can seem that some technology companies are in denial about its misuse."
The comments were backed by Downing Street as "important".
"The prime minister very much shares the view that's being expressed there around the use of web-enabled Internet access technologies by violent and extremist groups amongst others and the need to do more," David Cameron's official spokesman told reporters.
Government officials have held a series of meetings on the issue with firms such as Google and Facebook, most recently last month.
- 'Powers already immense' -
Campaigners said the security services already have ample access to online information.
Eric King, deputy director of Privacy International, called Hannigan's comments "disappointing".
"Before he condemns the efforts of companies to protect the privacy of their users, perhaps he should reflect on why there has been so much criticism of GCHQ in the aftermath of the Snowden revelations," he said.
"GCHQ’s dirty games -- forcing companies to hand over their customers’ data under secret orders, then secretly tapping the private fibre optic cables between the same companies' data centres anyway -- have lost GCHQ the trust of the public, and of the companies who services we use."
Eva Galperin of the Electronic Frontier Foundation, a non-profit organisation which campaigns for online civil liberties, also criticised the remarks.
"Their powers are already immense. I think that asking for more is really quite disingenuous," she told BBC radio.
In 2013, Cameron's government scrapped planned legislation dubbed a "snoopers' charter" which would have compelled mobile phone and Internet service providers to retain extra data amid opposition from coalition partners the Liberal Democrats.
But Home Secretary Theresa May has vowed to revive it if the prime minister's Conservatives win next May's general election outright.
Hannigan's comments came less than a week after he started work with GCHQ's reputation in the spotlight after Snowden's revelations.
In a farewell speech last month, his predecessor, Iain Lobban, launched a robust defence of GCHQ staff, saying their mission was "the protection of liberty, not the erosion of it".
Britain is on a high state of alert due to the fear of attacks linked to the IS group in Syria and Iraq, where it is taking part in international air strikes.
In August, Britain's threat level from international terrorism was raised to severe, the second highest level, meaning that an attack is thought to be highly likely.
Police said last month they were taking down around 1,000 pieces of illegal content from the Internet every week including videos of beheadings and torture.