Internet companies are being given one month to show they are taking serious action to limit the availability of terrorist propaganda online.
At a special meeting in New York on Wednesday, world leaders including Theresa May will challenge the companies to develop technological fixes to take down terrorist material within one to two hours.
The moves come amid widespread concerns about the dominance of online media players Google and Facebook. Press Gazette’s Duopoly campaign has warned that by taking most of money spent on digital advertising in the UK they are forcing news publishers out of the market.
It has been argued that Google and Facebook take advertising revenue without having to pay for any content or take legal responsibility for it.
Interior ministers from the G7 group of leading nations will meet in Rome on 20 October to decide whether enough progress has been made.
And governments are making clear they are ready to take legislative action which could include fines for internet giants which fail to act.
In her keynote speech to the United Nations General Assembly in New York, May will say it is time to step up efforts to tackle extremists’ use of the internet and block access to ideologies which “preach hatred, sow division and undermine our common humanity”.
She will hail the shows of solidarity and resilience shown by communities in Manchester and London following terror attacks this year.
But she will say: “Defiance alone is not enough. As Prime Minister, I have visited too many hospitals and seen too many innocent people murdered in my country.
“When I think of the hundreds of thousands of victims of terrorism in countries across the world, I think of their friends, their families, their communities, devastated by this evil.
“And I say enough is enough.”
The Islamic State terror group has developed a more sophisticated use of social media than earlier militants like al Qaida, disseminating more than 27,000 items through outlets like Twitter in a five-month period between January and May this year.
Links to material ranging from bomb-making instructions to videos glamorising the group and calls to commit atrocities with cars and knives in Western cities are spread rapidly, with the majority of shares taking place in the first two hours.
Experts believe that by removing links more quickly, access to the material can be dramatically reduced, even if it takes longer to eradicate every trace of it from sites like YouTube.
Some of the world’s biggest tech companies, including Facebook, Microsoft and Twitter, will take part in the event hosted by Mrs May, French President Emmanuel Macron and Italian PM Paolo Gentiloni, on the fringe of the General Assembly.
Also present will be major advertisers, who are starting to put pressure on the internet giants to stop ads being screened alongside unacceptable material.
May will hail progress made by tech companies since the establishment in June of an industry forum to counter terrorism.
But she will make urge them to go “further and faster” in developing artificial intelligence solutions to automatically reduce the period terror propaganda remains available and eventually prevent it appearing at all.
Britain, France and Italy will come together behind a target of one to two hours to take down terrorist content wherever it appears.
One Downing Street source said the companies “have been doing something, but just not enough”.
The source said: “These companies have some of the best brains in the world. They should really be focusing that on what matters, which is stopping the spread of terrorism and violence.
“We want them to break the echo chambers.”
In her address to the UN, Mrs May will say: “When terrorists struck London and Manchester this year, the world saw our cities come together in defiance.
“Our Parliament carries on. Ariana Grande came back to Manchester and sang again. London Bridge is bustling with people. Our communities came together at the mosque in north London. And Londoners got back on the Tube.
“The terrorists did not win, for we will never let anyone destroy our way of life.
“But defiance alone is not enough. In the last decade hundreds of thousands have been killed by terrorists across the world. This is a truly global tragedy that is increasingly touching the lives of us all.”
Pledging to continue to “take the fight” to terrorists, Mrs May will add: “U ltimately it is not just the terrorists themselves who we need to defeat. It is the extremist ideologies that fuel them. It is the ideologies that preach hatred, sow division and undermine our common humanity.”
Google and YouTube have already announced they are increasing their use of technology to help automatically identify offending videos, while Facebook has said it is looking at automated identification of terrorist material.
Twitter suspended 299,649 accounts between January 1 and June 30 this year, 75 per cent of which were blocked before their first tweet.
Facebook has said publicly that it is looking at developing artificial intelligence to automate the identification of terrorist material.
Speaking before the New York event, May called for “a fundamental shift in the scale and nature of our response both from industry and governments” and called on leaders from around the world to join Britain, France and Italy in demanding action.
Among tech executives expected to take part in the event are Google general counsel Kent Walker, Facebook’s head of global policy Monika Bickert, Microsoft vice-president David Heiner, and Twitter’s public policy manager Lauren Culbertson.
A spokesman for the Global Internet Forum to Combat Terrorism, which brings together tech companies, said: “Combating terrorism requires responses from government, civil society and the private sector, often working collaboratively.
“The Global Internet Forum to Counter Terrorism was founded to help do just this and we’ve made strides in the past year through initiatives like the Shared Industry Hash Database.
“We’ll continue our efforts in the years to come, focusing on new technologies, in-depth research, and best practices.
“Together, we are committed to doing everything in our power to ensure that our platforms are not used to distribute terrorist content.”