Web giants YouTube, Facebook,Twitter and Microsoft will step up efforts to remove extremist content from their websites by creating a common database.
The companies will share 'hashes' - unique digital fingerprints they automatically assign to videos or photos - of extremist content they have removed from their websites to enable their peers to identify the same content on their platforms.
"We hope this collaboration will lead to greater efficiency as we continue to enforce our policies to help curb the pressing global issue of terrorist content online," the companies said in a statement on Tuesday.
Tech companies have long resisted outside intervention in how their sites should be policed, but have come under increasing pressure from Western governments to do more to remove extremist content following a wave of militant attacks.
YouTube and Facebook have begun to use hashes to automatically remove extremist content.
But many providers have relied until now mainly on users to flag content that violates terms of service. Flagged material is then individually reviewed by human editors who delete postings found to be in violation.
Twitter suspended 235,000 accounts between February and August this year and has expanded the teams reviewing reports of extremist content.
Each company will decide what image and video hashes to add to the database and matching content will not be automatically removed, they said.
The database will be up and running in early 2017 and more companies could be brought into the partnership.
The European Union set up an EU Internet Forum last year bringing together the internet companies, interior ministers and the EU Counter-Terrorism Coordinator to find ways of removing extremist content.
