There have been more arrests in Britain following a vehicle and stabbing attack that killed at least seven people and injured dozens more in London at the weekend.
Police reportedly know the identities of the three alleged perpetrators, killed by police after what has been deemed the third terrorist attack in three months in the country.
It follows an attack on London's Westminster Bridge in March and another in the city of Manchester two weeks ago.
Prime Minister Theresa May has chaired an emergency meeting of cabinet and says the attackers' methods are evolving.
"In terms of their planning and execution, the recent attacks are not connected. But we believe we are experiencing a new trend in the threat we face as terrorism breeds terrorism and perpetrators are inspired to attack not only on the basis of carefully constructed plots after years of planning and training, and not even as lone attackers radicalised online, but by copying one another and, often, using the crudest of means of attack. We cannot and must not pretend that things can continue as they are."
Ms May says Thursday's general election will not be cancelled in response.
And she has called for a tougher approach on national security.
"While we have made significant progress in recent years, there is, to be frank, far too much tolerance of extremism in our country. So we need to become far more robust in identifying it and stamping it out across the public sector and across society. The whole of our country needs to come together to take on this extremism, and we need to live our lives not in a series of separated, segregated communities, but as one truly united kingdom."
Resuming his campaign after a temporary break, opposition leader Jeremy Corbyn says a future Labour government would recruit thousands of police and security services staff.
He has also criticised cuts to law enforcement during Ms May's previous tenure as Home Secretary.
"You cannot protect the public on the cheap. The police and security services must get the resources they need, not 20,000 police cuts. Theresa May was warned by the Police Federation, but she accused them of crying wolf."
Mr Corbyn says "difficult conversations" with some other governments are needed.
"Our democratic values must be maintained. We must resist Islamophobia and division and turn out on 8 June united in our determination to show our democracy is strong, however you decide to vote. And, yes, we do need to have some difficult conversations, starting with Saudi Arabia and other Gulf states who have funded and fuelled extremist ideology. It's no good Theresa May suppressing a report into the foreign funding of extremist groups. We have to get serious about cutting off their funding to these terror networks, including ISIS here and in the Middle East."
German chancellor Angela Merkel, French president Emmanuel Macron and Russian president Vladimir Putin are among those expressing condolences and solidarity.
United States president Donald Trump used the occasion to criticise London mayor Sadiq Khan's response that there was no reason for Londoners to be alarmed.
On the social media platform Twitter, Mr Trump also renewed his call for a Muslim travel ban.
Mr Khan's team dismissed the comments, saying he has more important things to do than respond to Mr Trump, who they say deliberately took the remarks out of context.
In Australia, the Government has confirmed at least three Australian citizens were caught up in the attack.
One is reportedly a 30-year-old Brisbane woman who survived a knife wound to her neck.
Foreign Minister Julie Bishop has told the ABC she is receiving hospital treatment.
"We can confirm that three Australians have been affected. One is currently in hospital, but she's recovering and I've spoken to her father. Another man who, I understand, received stitches is on his way back to Australia. I believe he's been speaking to the media. And there is a third Australian. We're still making inquiries with respect to the circumstances of the third Australian."
The injured man has been identified as a Darwin electrician, Andrew Morrison.
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