Six people were killed and several others injured when a van mowed down pedestrians on London Bridge and three attackers proceeded to stab pub-goers at the nearby Borough Market.
Police said counter-terrorism officers raided several addresses in Barking, an east London suburb, and arrested 12 people there Sunday morning in connection with the attack. "Our prayers are with all in London", the police department's official news account tweeted, along with a picture of three heavily armed officers and a police dog in Times Square. In March, a lone assailant rammed into pedestrians on Westminster Bridge and then stabbed a police officer outside Parliament.
Armed officers also conducted a raid in the East Ham area of the city.
The three attackers on Saturday night were wearing what looked like explosive vests that were later found to have been fake. Grande and other stars planned to perform Sunday night at a benefit concert for victims under tight security in Manchester.
"We don't believe there are additional elements" at large, said Home Secretary Amber Rudd.
He replied: "I'm not happy with a shoot-to-kill policy in general, I think that is quite risky and I think can often be counterproductive".
Kimberley Del Toro said that her daughter had been unable to speak since sustaining the wound.
Residents reported hearing loud bangs and said they were later told by police they were controlled explosions.
"In the wake of yet another attack, of more loss of life and of more families devastated by terror, every one of us will once again feel the now too familiar sense of horror and helplessness".
Medics treated the injured near the market as shocked people cried and shouted around them.More news: United States university students walk out of vice-president's speech
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Security cordons will remain around London Bridge indefinitely.
Mayor of London Sadiq Khan asked "all Londoners and visitors to our city to remain calm and vigilant".
The three suspects in yesterday's attack were shot dead by cops after they ploughed into pedestrians on the bridge in a white B&Q van.
Speaking outside Downing Street on Sunday morning after chairing a committee of the emergency Cobra committee, Theresa May said Britain "cannot and must not pretend that things can continue as they are" following the third terror attack in the United Kingdom within four months.
"They went "this is for Allah" and they had a woman on the floor, they were stabbing her", said witness Gerard Vowls.
Describing the scene outside of Applebee's, the establishment in which she took refuge, Ms Owen said: "It was horrible, horrible". Police officers yelled at people to run from the area, and blasts were heard as officers performed a series of controlled explosions.
In Taiwan, both the Tourism Bureau and the Travel Agent Association (TAA) said they had not received reports about any deaths or injuries of Taiwanese in the attack.
The image spread like wildfire across Twitter and British newspapers said the man, whose identity is unknown, was a symbol of defiance.
"Someone said, 'What is going on?' and one of the people running said, 'There is a man with a knife up there and he is coming this way.' There was complete panic as everyone ran to the back of the restaurant and crouched down trying to hide themselves from view", one witness told CNN.
Facebook said it did not allow groups or people that engage in terrorist activity or posts that support terrorism.