Prime Minister Theresa May has been warned that her promise to tighten regulation on tech firms after the London attacks will not work.
Mrs May said areas of the internet must be closed because tech giants provided a “safe space” for terrorist ideology.
Twitter, Facebook and Google said they were investing heavily in the area.
An internet advocacy group said social media was not the problem, while an expert in radicalisation branded Mrs May’s criticism “intellectually lazy”.
Google, which owns Youtube, along with Facebook, which owns WhatsApp, and Twitter were among the tech companies already facing pressure to tackle extremist content, a pressure that intensified on Sunday.