The attacker was born in Britain and had been investigated for links to religious extremism, British Prime Minister Theresa May said. British officials did not release the attacker's identity or confirm a link with the Islamic State group.

LONDON — The Islamic State group claimed responsibility for an attack by a man who plowed an SUV into pedestrians on London's Westminster Bridge before stabbing a police officer to death on the grounds of Parliament, and the investigation shifted Thursday to a city in central England long known as an incubator for radicalism.

 

The attacker was born in Britain and had been investigated for links to religious extremism, British Prime Minister Theresa May said in a sweeping speech to lawmakers in which she also encouraged people in London to go about their lives. At least eight people were arrested in raids, some in the central city of Birmingham.

 

The Islamic State group said through its Aamaq News Agency that the 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. In addition to the police officer and the attacker, who was shot by police, two people died on Westminster Bridge and at least 30 others were injured, seven critically.

 

British officials did not release the attacker's identity or confirm a link with the Islamic State group. May described it as "a perversion of a great faith."

 

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. The London attack echoed vehicle rampages in Nice, France, and Berlin last year that the group claimed under its banner.

 

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 lawmakers. "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.

 

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.

 

The raids took place in a major thoroughfare of Birmingham that is rundown, mostly Muslim and relatively poor.

 

Many suspects in British terror attacks and plots have roots in the city described in a recent terror analysis as a hotbed of 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.