Theresa May has warned internet giants she will keep up the pressure over their failures to deal with extremist material being posted online.
Companies like Google have made some progress in tackling terror and hate being spread in cyberspace but they must do more, the Prime Minister said.
Information on how to mount a terror attack was found to be easily accessible online in the wake of the Westminster atrocity last month.
Mrs May said: "The Government has already spent quite a lot of time talking with the companies about what they can do and what we think they should be doing. They have made some progress.
"Obviously we've had - there's a significant number of pieces of material taken down from the internet through the counterterrorism internet referral unit, something like a quarter of a million pieces since 2010 now.
"We continue to talk to the companies. The Home Secretary met them last week.
"We think that there is more that they could and should be doing and we will be continuing to encourage them to do more.
"I think it's very important that we do see action from the companies. We will continue to press them to make sure, because as we know, material on the internet can have an impact when it is seen by other people."