There must be “no place for terrorists to hide” and intelligence services must have access to encrypted messaging services, the home secretary has said.
It comes after it emerged that Khalid Masood was reportedly on the messaging app WhatsApp two minutes before an attack in Westminster in which he killed four people.
Police are unable to read his messages.
But labour leader Jeremy Corbyn said there was a balance between the “right to know” and “the right to privacy”.
Amber Rudd said she would be asking tech firms to “work with us” when she meets with them this week.
Speaking to BBC One’s Andrew Marr programme, Ms Rudd said: “We need to make sure our intelligence services have the ability to get into situations like encrypted WhatsApp.”
Encryption is a way of scrambling computer data so it can only be read by the people you want to see it.
All messages sent on WhatsApp have end-to-end encryption.
This means messages are unreadable if they are intercepted by anyone, including law enforcement.
The Facebook-owned company, which has a billion users worldwide, has said protecting private communication was one of its “core beliefs”.
Asked if there was an issue about giving the security services more powers to hack in to messaging services like WhatsApp, Mr Corbyn told ITV’s Peston on Sunday they already had “huge powers” of investigation.
But writing in the Sunday Telegraph, the home secretary said she was asking companies like Google, Twitter and Facebook to be more “proactive” in tackling extremism.
In the Sunday Times, Foreign Secretary Boris Johnson also called for internet companies to develop technology to detect and remove extreme material.
The calls come after Wednesday’s terror attack when attacker Masood ran down pedestrians and fatally a stabbed police officer who was guarding the houses of Parliament.
In total five people died – including the attacker who was shot by police – and 50 others were injured, two seriously.
On Saturday the Metropolitan police said they believed Masood acted alone. But they added they were also “determined” to find out whether he had been was inspired by terrorist propaganda.
Ms Rudd said: “Each attack confirms again the role that the internet is playing in serving as a conduit, inciting and inspiring violence, and spreading extremist ideology of all kinds…
“We need the help of social media companies, the Googles, the Twitters, the Facebooks of this world.
“And the smaller ones, too: platforms such as Telegram, WordPress and Justpaste.it.
“We need them to take a more proactive and leading role in tackling the terrorist abuse of their platforms.
“We need them to develop further technology solutions.”
Mr Johnson attacked internet giants for their “disgusting” failure to remove extremist material.
He said: “They are not acting when they are tipped off.
“Evil flourishes when good men do nothing – and that’s what’s happening here.
“They are putting up adverts next to it.”
Earlier this month, Google’s European boss apologised after adverts from major firms and government agencies appeared next to extremist content on its YouTube site.
Matthew Brittin promised to review the firm’s policies and strengthen enforcement.
Marks and Spencer and Audi were among the companies that pulled their online adverts over the issue.
WhatsApp must not be ‘place for terrorists to hide’}