The third attack in three months in London killed seven and wounded 48 others. A French and Canadian national were among those killed. Police arrest 12 suspects.
British Prime Minister Theresa May on Sunday called for a stronger response to extremism after an attack on London Bridge and nearby area killed seven people and injured 48 others.
On Saturday, three attackers drove a hired van into pedestrians on London Bridge then ran into the bustling Borough Market area where they stabbed numerous people.
The attack occurred five days before a parliamentary election and was the third to hit Britain in less than three months. May said Thursday's vote would go ahead.
"It is time to say enough is enough," the Conservative leader said outside her Downing Street office, where British flags flew at half-mast.
"We cannot and must not pretend that things can continue as they are," May said, calling for a beefed-up counter-terrorism strategy that could include longer jail sentences for some offences and agreements to regulate cyberspace.
Police shot dead the three male assailants in the Borough Market area near London Bridge within eight minutes of receiving the first emergency call shortly after 10 pm (2100 GMT).
May said the series of attacks were not connected in terms of planning and execution, but were inspired by what she called a "single, evil ideology" that had to be confronted both abroad and at home.
She also said that the internet and big internet companies provided the space for such extremism to breed.
There was no immediate claim of responsibility for London's latest attack.
TRT World's Francis Collings has more details.
12 suspects arrested
Mark Rowley, head of counter-terrorism police, said eight officers had fired about 50 bullets to stop the attackers, who appeared to be suicide bombers because they were wearing what turned out to be fake suicide vests.
"The situation these officers were confronted with was critical – a matter of life and death – three armed men, wearing what appeared to be suicide belts, had already attacked and killed members of the public and had to be stopped immediately," Rowley said.
A member of the public received non-critical gunshot wounds during the incident, he said.
London police arrested 12 people in the Barking district of east London in connection with the attack and raids were continuing there, the force said. A Reuters photographer saw another raid take place in nearby East Ham.
Foreigners among dead
A Canadian national was among those killed, Canadian Prime Minister Justin Trudeau said in a statement. None of the dead were identified by name.
French foreign miister Jean-Yves Le Drian said a Frenchman was among the seven people killed and seven more nationals of his country were wounded in the attack.
Australian authorities said nationals from their country were among those injured.
Second attack in two weeks
Less than two weeks ago, a suicide bomber killed 22 children and adults at a concert by US singer Ariana Grande in Manchester in northern England.
In March, in an attack similar to Saturday's, five people died after a man drove into pedestrians on Westminster Bridge in central London and stabbed a policeman.
After the Manchester attack, Britain raised its threat level to "critical" - meaning an attack is expected imminently - but downgraded it back to "severe", which means an attack is highly likely, on May 27.