Ms Archibald is the first person killed in the attack to be identified. Several of the almost 50 people wounded in the attack remain in a critical condition, police officials say. French and Australian authorities said nationals from their countries were among those injured.
Counterterrorism officers raided several addresses in Barking, an east London suburb, and arrested 12 people there Sunday, police said. We recently witnessed this after the attacks in Manchester and in the Westminster area of London.
May said that Britain was facing a new threat from copycat attacks, and "it is time to say 'enough is enough.'" She called for worldwide agreements to curb online extremism, said longer jail sentences might be needed for terrorism offenses and argued that there is "far too much tolerance of extremism in our country". One of those officers confronted one of the attackers with a baton.
Seven people were killed and 48 injured in the attack on Saturday, with 21 fighting for their lives in hospital. Wearing fake explosive vests, they then fled the van with large knives and attacked people in bars and restaurants.
"I saw a young girl being stabbed in the chest", he told LBC radio, recalling how the three "went randomly along Borough High Street stabbing people". Lewis Bennett told the Guardian newspaper:"People started screaming and running out the back door".
Sam said everyone sheltering in the Market Porter pub on Park Street dropped to the ground, saying: "I called the police and told them what I had seen and the mayhem outside".
According to Mark Rowley, a senior officer in London's Metropolitan Police Service, eight officers fired upwards of 50 rounds at the attackers.
This is the third attack in Britain in as many months.
The minister tweeted that he was traveling to London on Monday.
Community leaders urged calm, but at Speakers' Corner in London's Hyde Park - one of the capital's most famous places for public speaking - there was evidence of growing tensions in the capital as a Muslim speaker holding a copy of the Quran was denounced by some passers-by as "a disgrace" after the events of Saturday night. "If we don't get smart it will only get worse", Trump tweeted. The critical level means another attack could be imminent.
"And there was another guy, who was probably in his 40s, standing on the other side of the ambulance knocking on the other window, saying "I've been stabbed" and he was covered in blood".
Prime Minister May, who served as interior minister for six years before taking office after the Brexit vote last summer, said Britain's response to the terror threat must change.
The general election will go ahead as planned on Thursday.
Saturday's rampage is the latest in a string of attacks to hit Europe, including in Paris, Berlin and Saint Petersburg, and the French, German and Russian leaders sent messages of support.
"Did you notice we are not having a gun debate right now?" "GOD BLESS!" - and highlighting his thwarted ban on travellers from six mainly Muslim countries.
In this Saturday, June 3, 2017, image made from a video, people run from the scene an attack in London.
Former vice president and 2000 Democratic presidential nominee Al Gore said on CNN's "State of the Union: "I don't think that a major terrorist attack like this is the time to be divisive and to criticize a mayor who's trying to organize his city's response to this attack".
"I was sat by the window and peered out through the frosted glass, and saw three men, two of which with large knives covered in blood, chasing a man through Borough Market".
"In two or five seconds, they shot all the three men down", Sciotto told the BBC.
In March, five people died after an attacker drove a vehicle at pedestrians on Westminster Bridge and stabbed a policeman in the grounds of parliament.