The Prime Minister said tech giants have provided a “safe space” for terrorist ideology and called for areas of the internet to be closed after Saturday night’s attack.
The so-called Islamic State group has claimed responsibility for the attack at London Bridge, which killed seven people and injured 48.
Tech giants working to rid networks of terrorist activity...
Google, owner of YouTube, said it has invested heavily to combat extremist content after several clients pulled advertising over the issue.
Marks and Spencer Group Plc (LON:MKS), HSBC Holdings (LON:HSBA), Sky plc (LON:SKY) are among those who boycotted advertising after their marketing content appeared alongside YouTube videos that advocated extremism.
A spokesman for Google said the search engine was working on an "international forum to accelerate and strengthen our existing work” to fight abuse on its platforms, adding that it shared the government’s commitment to ensuring terrorists don’t have a voice online.
"We are committed to working in partnership with the government and NGOs (non-governmental organisations) to tackle these challenging and complex problems, and share the government's commitment to ensuring terrorists do not have a voice online,” he said.
"We employ thousands of people and invest hundreds of millions of pounds to fight abuse on our platforms and ensure we are part of the solution to addressing these challenges."
Simon Milner, director of policy at Facebook, said: "Using a combination of technology and human review, we work aggressively to remove terrorist content from our platform as soon as we become aware of it - and if we become aware of an emergency involving imminent harm to someone's safety, we notify law enforcement."
Nick Pickles, UK head of public policy at Twitter, said terrorist content had “no place” on the platform and has shut down 376,890 accounts linked to extremism in the last six months of 2016.
"We continue to expand the use of technology as part of a systematic approach to removing this type of content,” he said.
"We will never stop working to stay one step ahead and will continue to engage with our partners across industry, government, civil society and academia."
Conservatives propose stricter approach to internet regulation...
A Tory manifesto have proposed a stricter approach to regulation of the internet, including tougher sanctions for companies that fail to remove illegal content and legislating for an industry-wide levy on social media companies to counter damaging activity online.
Digital campaigners the Open Rights Group said the Tory’s proposals could be risky as it could lead to extremist content being placed in “darker corners of the web” where they will be harder to observe.
"But we should not be distracted: the internet and companies like Facebook are not a cause of this hatred and violence, but tools that can be abused,” it said.
"While governments and companies should take sensible measures to stop abuse, attempts to control the internet is not the simple solution that Theresa May is claiming."
Professor Peter Neumann, director of the International Centre For The Study Of Radicalisation at King's College London, said: "Few people radicalised exclusively online. Blaming social media platforms is politically convenient but intellectually lazy.
"In other words, May's statement may have sounded strong but contained very little that is actionable, different, or new."
Twelve people were arrested, including seven women and five men aged between 19 and 60, in connection to Saturday's attack. Eleven remain in custody on suspicion of offences against the Terrorism act.
A white van hit pedestrians on London Bridge on Saturday evening before three men wearing fake bomb vests got out and stabbed people in nearby Borough Market. The attackers were shot dead by police.