4 Dead, Including Cop, in Terror Attack Outside UK Parliament: Officer Was 'Protecting Our Democracy'

A cop was stabbed to death and a suspect shot after car attack at British Parliament.

A knife-wielding man stabbed a police officer to death outside British Parliament Wednesday after several people were mowed down by a car on the Westminster Bridge, authorities said.

At least four people were killed, including  Metropolitan Police Constable Keith Palmer, and 40 were injured along the thoroughfare fronting London's Parliament, before the attacker was fatally shot by police.

The slain officer, a husband and father, had served for 15 years and was a member of the Parliamentary and Diplomatic Protection Command.

Read: Brussels Bombing Supect Know as the 'Man in the Hat,' Arrested in Belgium

"Keith Palmer was killed while bravely doing his duty - protecting our city and the heart of our democracy from those who want to destroy our way of life," said London Mayor Sidiq Khan in a statement. 

Mark Rowley, acting deputy commissioner at Scotland Yard, praised the 48-year-old officer as "someone who left for work today expecting to return home at the end of his shift and he had every right to expect that would happen."

Prime Minister Theresa May was bundled into a car by plain-clothes security officers and whisked from the scene. She later called the attack "sick and depraved."

The attack occurred on the anniversary of last year's terrorist bombing attacks in Brussels that killed 32 people and injured more than 300 others. ISIS later claimed responsibility. British authorities have thus far identified no suspects in Wednesday's violence.  

A woman with serious injuries was pulled from the Thames River, authorities said, and may have jumped to avoid being hit by the vehicle speeding down the bridge's sidewalk.

Surveillance video shows woman hitting the Thames at about the 12-second mark.

Foreign Minister Tobias Ellwood, a military veteran, performed CPR on the wounded policeman as he lay bleeding to death on the cobblestones outside Parliament. 

Parliament members took to social media to praise the slain policeman who guarded the historic compound. 

"It is utterly devastating to know that a police officer lost his life protecting us and our Parliament. They are the best and the bravest," said MP Conor McGinn on Twitter. 

Scotland Yard reported there were at least 40 injuries, including three police officers. Several tourists were among the wounded, police said. 

Residents were told to avoid several central locations including Parliament, Victoria Street and Whitehall, a historic road leading from Trafalgar Square to the national seat of government.  

 #LondonAttack pictures. pic.twitter.com/kuZzKvaS72

The attacker was able to breach the perimeter of the lawmaking house and was shot several times after stabbing Palmer.

Witnesses described seeing bloodied victims and bodies lying on the pavement and hearing screams from the injured. Police ordered people to run from the heavily trafficked tourist area, also home to Big Ben, during the violence. 

Read: Brother of Brussels Suicide Bomber Headed to Rio Olympics

“It was horrendous, just horrendous,” one woman at the scene told journalists.

 #LondonAttack update: Reports of civilians 'mowed down' on Westminster Bridge; Air ambulance on scene [pics, video] https://t.co/Gq6YvVNZGv pic.twitter.com/sdjeLV6Ne3

Areas around Parliament remained on lockdown Wednesday night..

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