Photo: The Canadian Press

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 sombre but defiant statement, Britain's prime minister declared that "we are not afraid."

In a sweeping speech before the House of Commons, British Prime Minister Theresa May said the man who killed three people Wednesday before being shot to death by police was born in Britain and once came under investigation for links to religious extremism.

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 29 others were hospitalized, seven critically. Others were injured and treated at the scene.

May set an unyielding tone Thursday, saluting the heroism of police as well as the ordinary actions of everyone in the British capital 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."

IS said Thursday 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 countries fighting IS in Syria and Iraq.

Police believe the London attacker acted alone and there is no reason to believe "imminent further attacks" are planned, May said, adding that he had been investigated before but police believed he was a peripheral figure at the time.