Twitter does not pro-actively alert authorities to terrorist content posted by users despite the site being used by supporters of Islamic State, a senior executive has said.
Nick Pickles, UK public policy manager at the microblogging site, suggested material was visible because it was a public platform.
It also emerged that Google is planning to introduce a scheme which could see those who put extremist-related entries into its search engine being shown anti-radicalisation links as part of attempts to highlight “counter-narratives”.
Social media firms have come under scrutiny after Islamic State built up a vast online propaganda machine.
Officials estimate there are more than 50,000 Twitter accounts used by supporters of the terror group, also known as Daesh, Isil or Isis.
Appearing before the Commons Home Affairs Committee, Pickles and representatives from Google and Facebook were asked about the thresholds they apply on notifying authorities about terrorist material identified by staff or users.
Labour MP Chuka Umunna asked: “What is the threshold beyond which you decide… that you must pro-actively notify the law enforcement agencies?”
Dr Anthony House, of Google, and Simon Milner, of Facebook, said their threshold was “threat to life”.
Pickles said: “We don’t pro-actively notify. One of the things… because Twitter’s public, that content is available so often it’s been seen already.
“Then law enforcement have established criteria to come to us and then request information.”
He said proposals to introduce a legal requirement on sites in the US were not supported by authorities there.