Tech giants and governments must work together to stop terrorist atrocities being live streamed on social media, Theresa May will tell world leaders.
The Prime Minister will say governments need to learn lessons following the Christchurch massacre in March, which was broadcast on the internet.
She will address leaders at the G20 summit in Osaka on Friday, highlighting action already being carried out by tech firms to remove terrorist content.
But she will call for closer collaboration between security officials and social media firms to prevent footage being posted in the first place, with a crisis hotline to raise concerns.
Mrs May is expected to say: “We should do all we can to bring the best minds together across industry to develop technology to tackle the misuse of live-streaming.
“We’ve seen the damage when terrorists can advertise into people’s homes – now we mustn’t let them broadcast their atrocities in real time.”
The attack on two mosques in Christchurch, New Zealand left 51 dead.
Australian Brenton Tarrant has pleaded not guilty to the murders and a terrorism charge and will stand trial next year.
New Zealand’s Jacinda Ardern and France’s Emmanuel Macron were joined by leaders including Mrs May and some of the world’s biggest tech firms in agreeing the Christchurch Call pledging action in the wake of the massacre.
At the G20 summit, Mrs May will highlight a new crisis response mechanism which is being developed by technology companies and supported by the UK and others as part of the Christchurch Call.
This will ensure that companies have established networks of “online first responders”, who are directly linked to government counter-terrorism units and law enforcement agencies.
The crisis hotline could be used to share “digital fingerprints” identifying harmful content which could allow companies to prevent the re-upload of existing terrorist material on to their platforms.
Mrs May is expected to tell world leaders: “There are no easy answers but I am sure that by combining different methodologies to detect illegal and harmful content we will be able to find an approach that severely limits terrorists ability to live stream.
“In the UK we are encouraging social media companies to develop these techniques at pace. Others should do the same.”
The work will build on efforts started through the Global Internet Forum to Counter-Terrorism (GIFCT).
GIFCT was created in the aftermath of the Westminster terror attack and the companies involved, Facebook, Google, Twitter and Microsoft, are already make use of technology to automatically remove terrorist propaganda.
GIFCT has already worked with over 100 smaller platforms but Mrs May will say tools and expertise need to be shared with others to build the capacity of industry to tackle terrorist content online.