Facebook blocks one million messages promoting terrorism or radical ideologies every week, says the head of the United Nations counter-terrorism committee.
Speaking at UN headquarters after a meeting with the private sector, Jean-Paul Laborde said YouTube had cancelled at least 14 million videos of terrorist propaganda in the past two years.
The UN must learn to move through social networks at the same speed, or faster, than terrorist organisations, he said.
But he warned there needed to be a balance between ensuring freedom and privacy online, while protecting the lives of all the world's citizens.
Maintaining that balance was "a great challenge" for law enforcement, civil society and private companies, Mr Laborde said.
The UN must first defeat terrorist organisations such as Islamic State on the internet and social networks.
To achieve those goals new relationships and connections must be forged between civil society, UN members and private enterprises such as Facebook, Google, Microsoft and Twitter, which control exchange of information online, he said.
"Private companies do not want to look like the bad guy and are doing much to help."
Earlier this month Facebook confirmed that comments praising Islamic State were posted to an account on the social media website established by one of the San Bernadino mass shooting suspects, Tashfeen Malik, under an alias.
However, it was uncertain whether the comments were posted by her or someone with access to her page.
The FBI said the comments included a pledge of allegiance to IS.
At the time, a Facebook Inc spokesperson said the profile was removed by the company for violating its community standards barring promotion or praise for "acts of terror."