David Cameron has vowed to "put the heat on" the internet companies over the online posting of pornographic images of children.
The prime minister said the internet firms were still not doing enough to take down such pictures even though they are illegal.
He called on the firms to work with the police to help prosecute those people responsible for putting them on the web.
His comments came as culture secretary Maria Miller prepares to chair a Westminster summit on Tuesday organised by Tory MP Claire Perry, who acts as the prime minister's adviser on the issue of children and pornography.
Cameron said that the posting of illegal images of children would be one of the key issues on the agenda.
"I'm not satisfied that internet companies do enough to help take them down," he told Sky News's Murnaghan programme.
"That's why we're having this round table in government with them to really put the heat on and say: 'Look, you've got extraordinary capabilities to help search the internet ... Work with the police, work with us so we can get these images off the internet and prosecute those who put them there.'
"That's issue number one and absolutely vital."
Cameron said that he also wanted to improve the ability of parents to ensure their children could not access unsuitable material online.
"We need to make more progress on this issue of explaining to everybody that we want to have better filters that parents can switch on to stop access to certain sites and material," he said.
"Again, the Government has been on this for the last three years. One of the things that's now happening is a lot of public Wi-Fi in Starbucks and elsewhere, public Wi-Fi, blocks access to certain sites, so we are making progress.
"But the world has changed so fundamentally with the internet that we've got some real threats there to our children and also from this appalling scourge of child pornography, we've to take a lot of action."
Cameron spoke as Google - which has come under fire for failing to do enough to tackle child porn - donated 5 million US dollars (£3.2 million) to further child protection.
Last week the internet giant announced it was giving £1 million to Internet Watch Foundation (IWF), a charity responsible for policing criminal content on the internet.
Today Google said it would split the additional cash between organisations in the US, Belgium, Canada, Australia and Latin America, and announced it would set up an additional 2 million US dollars (£1.3 million) Child Protection Technology Fund to help develop tools to combat child abuse images online.
Scott Rubin, director of communications and public affairs at Google, said: "We have a zero tolerance attitude to child sexual abuse imagery online. The fight to remove these images from the internet is a global one, and we hope these measures will help in that important battle."