LONDON, England -- The Islamic State group claimed responsibility Thursday for an attack by a man who plowed an SUV into pedestrians on one of London's famous bridges and then stabbed a police officer to death at Britain's Parliament. In a somber but defiant statement, Britain's prime minister declared that "we are not afraid."
The man who killed four people Wednesday and was shot to death by police was born in Britain and once came under investigation for links to religious extremism, British Prime Minister Theresa May said Thursday in a sweeping speech before the House of Commons.
British officials named the attacker as Khalid Masood, a 52-year-old with criminal convictions who was living in the West Midlands, which includes the central city of Birmingham.
Police raided properties in London and Birmingham, and made eight arrests.
A Utah man visiting London with his wife for their 25th anniversary and a British woman who was a school administrator were killed by the SUV attack on Westminster Bridge and at least 29 others were hospitalized, seven critically.
May set an unyielding tone Thursday, saluting the heroism of police as well as the ordinary actions of everyone who went about their lives in the aftermath.
"As I speak millions will be boarding trains and airplanes to travel to London, and to see for themselves the greatest city on Earth," she told the House of Commons. "It is in these actions - millions of acts of normality - that we find the best response to terrorism -a response that denies our enemies their victory, that refuses to let them win, that shows we will never give in."
Parliament began its moment of silence at 9:33 a.m., honoring the shoulder number of the slain officer, Keith Palmer, a 15-year veteran of the Metropolitan Police and a former soldier. Then Parliament, which was locked down after the attack, returned to business - a counter to those who had attacked British democracy.
In 1,000-year-old Westminster Hall, the oldest part of Parliament's buildings, politicians, journalists and parliamentary staff lined up to sign a book of condolences for the victims. Among them was a uniformed policeman, who wrote: "Keith, my friend, will miss you."
The rampage was the first deadly incident at Parliament since 1979, when Conservative lawmaker Airey Neave was killed in a car bombing by Irish militants.
Some parliamentarians said they were shaken, and all were somber. But they were also determined.
"There is no such thing as 100 percent security," said Menzies Campbell, a member of the House of Lords. "We have to learn to live with that."
The London attack echoed deadly vehicle rampages in Nice, France, and Berlin last year that IS has claimed.
The Islamic State group said through its Aamaq News Agency that the London attacker was a soldier of the Islamic State who "carried out the operation in response to calls for targeting citizens of the coalition" of countries fighting IS in Syria and Iraq.
The IS group has been responsible for numerous bloody attacks around the globe and has specifically called for Western followers to carry out this kind of attack in their own countries, though the group has also claimed events later found to have no clear links to it.
Police believe the attacker acted alone and there is no reason to believe "imminent further attacks" are planned, May said. He had been investigated before but police believed he was a peripheral figure, May said.
Labour Party lawmaker Khalid Mahmood, who represents part of Birmingham, condemned the "barbaric attack" and urged his fellow Muslims to report concerns about radicalization to the police.
"We have to condemn this outright," he said. "There are no ifs or buts. This is a hugely tragic incident. These people do not belong to any faith. They certainly don't belong to my faith of Islam."
Mahmood said the attacker and those like him "should be condemned by everybody and this shouldn't serve as a tool for division within our community."
Many suspects in British terror attacks and plots have roots in the city, which has been described in a recent terror analysis by the Henry Jackson Society conservative think tank as a center for Islamist extremism. Several local mosques have also been linked to extremist clerics.
British security forces have foiled 13 plots in the past four years. There are currently thousands of extremists in the U.K. who are known to officials but only a fraction of whom are under surveillance, according to a security official who spoke on condition of anonymity because he was not authorized to speak about ongoing security operations. It takes dozens of officers to watch just one terror suspect.
Witnesses said the attacker went straight after the police officer after ramming into the pedestrians.
"This man got out of the car with two knives in his hands and while he was running he was stabbing people. He arrived in front of the entrance to the parliament and he started to stab a policeman," said Vincenzo Mangiacarpe, an Italian boxer who was visiting Parliament. "You can imagine if someone was playing a drum on your back with 2 knives - he gave him around 10 stabs in the back, then he left the policeman and he came toward us."
Metropolitan Police counterterrorism chief Mark Rowley revised the death toll from five to four, including the attacker. He said 29 people required hospitalization and seven of them were in critical condition. He also said that authorities were still working out the number of "walking wounded." Police had previously given the total number of wounded in Wednesday's attack as around 40.
May said people from 11 countries were among the victims. They included 12 Britons, three French, two Romanians, four South Koreans, one German, one Pole, two Irish, one Chinese, one Italian, one American and two Greeks required hospital treatment.
Kurt Cochran, a Utah man visiting London with his wife Melissa for their 25th anniversary, was named as among the dead by the Church of Jesus Christ of Latter-day Saints. She was seriously injured in the attack as is still hospitalized.
President Donald Trump was among the world leaders offering their condolences.
London has been a target for terrorism many times over past decades and the threat level for the British capital was already listed at severe, meaning an attack was "highly likely." Just this weekend, hundreds of armed police took part in an exercise simulating a "marauding" terror attack on a tourist boat on the River Thames.
May said the attack in London targeted "free people everywhere," and she said she had a response for those behind it: "You will not defeat us."
Associated Press Writers Paisley Dodds in Birmingham; Gregory Katz, Frank Griffiths, Lori Hinnant and Sophie Berman in London; and Bilal Hussein in Beirut contributed to this report.
ISIS claims responsibility for London attack; UK's May defiant