Police investigating the deadliest terror attack in central London in 12 years have arrested eight people and conducted raids at six addresses around Britain, as Prime Minister Theresa May revealed the attacker was British born and once investigated for extremism.
May told MPs that the attacker was known to police, but did not identify him. She said he was a "peripheral figure."
Britain's most senior counterterror police officer said inquiries were continuing in London, Birmingham and elsewhere after a lone attacker plowed a car into crowds of people before stabbing a police officer dead in the grounds of the UK Parliament.
The first civilian victim was identified as a teacher, Aysha Frade, originally from Spain.
Investigation gathers pace
Mark Rowley, the lead officer in the UK for counter-terrorism policing, said hundreds of detectives worked through the night. Their investigation focused on the attacker's motivation, preparation and associates, he said.
"It is still our belief -- which continues to be borne out by our investigation -- that this attacker acted alone yesterday and was inspired by international terrorism," he said. "To be explicit, at this stage, we have no specific information about further threats to the public."
It was the first mass-casualty terrorist attack in Britain since 2005, when 52 people and four attackers died in the July 7 bomb attacks on the London public transportation system.
Rowley told journalists late Wednesday that police believe Wednesday's attack was an act of "Islamist-related terrorism," and indicated they knew the identity of the assailant but were not releasing his name.
Overnight, officers from the Metropolitan Police searched addresses in the city of Birmingham, in central England, and elsewhere and made a number of arrests, West Midlands Police said. "The arrests and searches were intelligence-led and there was no immediate risk to public safety," a statement said.
A UK official told CNN the working theory was that the attack was ISIS "inspired or copycat".
Khan told CNN that London was protected by the best police and security services in the world. "I'm confident that we are doing all that we can to keep our city safe, to keep Londoners safe and to keep visitors safe."
"London is the greatest city in the world. We will never be cowed by terrorism. We stand together, in the face of those who seek to harm us and destroy our way of life. We always have, and we always will," it said.
Tourists injured
The attacker, who rammed a car into pedestrians on Westminster Bridge before attempting to storm the Houses of Parliament, was shot dead at the scene. The area, the heart of the British government since the 16th century, was teeming with Londoners and visitors.
Rowley revised the number of dead down by one to three. The victims were a police officer protecting Parliament, a woman in her mid-40s and a man in his mid-50s, he said.
The mayor of Betanzos in northwest Spain, Ramon Garcia Vasquez, named the woman as Frade, 43, and told CNN that her family and relatives live in the town. Vasquez said Frade had lived in London for several years with her Portuguese husband.
"We are totally overwhelmed by the news and we send our condolences to the people in London," Garcia Vasquez added.
Twenty-nine people were treated in hospital, seven of whom are still in a critical condition, Rowley said. There were also a number of "walking wounded," he said.
A number of tourists were among 40 people hurt in the assault, including five South Koreans and three French high school students, according to officials from both countries. One Australian had been hospitalized, officials there said. A Chinese foreign ministry spokeswoman said one Chinese tourist was slightly injured.
A candlelit vigil will be held Thursday evening in Trafalgar Square, not far from Westminster, to show solidarity and remember the victims, the mayor's office announced.
The police officer who died was Keith Palmer, a 15-year veteran of the London police force, who was fatally stabbed on the grounds of Parliament before police killed his attacker. London police held a moment's silence Thursday morning to remember the attack victims.
One member of the government, Tobias Ellwood, was lauded as a hero after attempting to save Palmer.
