USA TODAY Editors

Three people — a police officer and two civilians — were killed and dozens wounded by a lone attacker near the United Kingdom's Parliament in London Wednesday. The attacker was shot and killed by police.

Here's what we know:

What happened?

The incident began when a man used a car to run down several pedestrians on the iconic Westminster Bridge. Two members of the public were killed by the vehicle and others were left with "catastrophic injuries," according to police and a hospital official. Three police officers were among those injured on the bridge.

The driver then rammed his car into the Parliament gates and fatally stabbed a police officer as he tried to enter the building.

Who was the attacker?

British Prime Minister Theresa May said Thursday that authorities know the identity of the attacker but did not name him.

She said the man was British-born and had been investigated by MI5, the domestic security agency, "some years ago" regarding concerns about violent extremism. "He was a peripheral figure. The case is historic – he was not part of the current intelligence picture," she said, adding that there was "no prior intelligence of his intent – or of the plot."

She said the suspect is believed to have been inspired by Islamist ideology.

Islamic State claims responsibility

ISIS claimed responsibility for the attack through its Aamaq news agency Thursday, calling the assailant a "soldier of the Islamic State." The claim couldn't immediately be verified.

Victims

British police said three people were killed — one police officer, a woman in her 40s and a man in his 50s. About 40 people, including three police officers, were wounded.

The Spanish Foreign Ministry identified the dead woman as Aysha Frade, a British national whose mother is Spanish.

The police officer was identified as Keith Palmer, 48. Palmer, a member of the Parliamentary and Diplomatic Protection Command, had worked as a police officer for 15 years.

British port officials pulled a Romanian woman from the Thames River after the attack. She was injured but alive.

Three French high school students were among the injured, according to French authorities. One of the injured people was American.The others were a mix of nationalities including from Romania, South Korea, Germany, Poland and Greece.

Multiple arrests made in raids

British police made multiple arrests Thursday in connection with the attack. Eight people were detained in raids on various addresses in London and Birmingham, central England. The car used in the attack — a gray Hyundai i40 — was hired from Birmingham, according to the BBC.

Brussels attack anniversary

Wednesday was the anniversary of suicide bombings in Brussels, Belgium, last year that killed 32 people and wounded hundreds. There is no evidence that the London attack was related. The London incident is another in a string of vehicle terror attacks in Europe.

In December, 12 people were killed and dozens wounded in a truck attack on a Berlin street market. In Nice, France, 86 died when a truck drove into a crowd gathered for Bastille Day fireworks. ISIS claimed responsibility for the attacks in France and Belgium.

What is happening at Parliament?

Parliament was placed on lockdown after the incident and people working there were eventually let out about five hours later on Wednesday evening. It resumed operations Thursday and lawmakers and others in the area held a minute's silence to honor the victims.

Where is Theresa May?

Prime Minister Theresa May was seen being ushered into a car at Parliament as the gun shots were being fired.

She called the incident a "sick and depraved terrorist attack" in a statement Wednesday. Speaking in Parliament on Thursday, she said it was "an attack on free people everywhere."

"A terrorist came to the place where people of all nationalities and cultures gather to celebrate what it means to be free. And he took out his rage indiscriminately against innocent men, women and children," she said.

"This was an attack on free people everywhere – and on behalf of the British people, I would like to thank our friends and allies around the world who have made it clear that they stand with us at this time."

How did world leaders react?

After being briefed by his national security adviser, President Trump spoke to May and called the incident "big news."

"We obviously condemn today's attack on Westminster, which the United Kingdom is treating as an act of terrorism," White House press secretary Sean Spicer said, adding that the U.S. would support British law enforcement officials.

In Paris, the lights of the Eiffel Tower were dimmed to pay respects to the victims. “Terrorism affects us all, and France knows the pain the British people are enduring today,” French President François Hollande said in a statement.

German Chancellor Angela Merkel, whose country had 12 people killed and dozens injured after a truck attack on a popular street Christmas market in December, equally condemned the attack and pledged her support.

"Even if the background of these actions is more precise awareness, I reiterate for Germany and its people: in the fight against any form of terrorism," Merkel said on Facebook. "We stand firmly and resolutely on the side of Great Britain."

After learning of the attack, Canadian Prime Minister Justin Trudeau expressed his shock and sadness, adding that Canadians were fully behind the people of the United Kingdom.

"Canadians stand united with the British people in the fight against terrorism," Trudeau said in a statement. "We will continue to work together with the U.K. and all our allies to show the world that freedom and democracy will always triumph.”

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