London attack: Assailant shot dead

A man killed four people, including a police officer, outside the UK Parliament on Wednesday in what British police are looking at as an act of "Islamist-related terrorism."

Scores more people were hurt when the attacker plowed his car through a crowd of people on a bridge over the River Thames, got out of his vehicle and fatally stabbed police officer Keith Palmer, a 15-year-veteran who was unarmed, on the grounds of Parliament.

An armed officer shot the assailant dead.

Mark Rowley, Britain's most senior counterterror police officer, told reporters late Wednesday that authorities believe they know the attacker's identity but are not releasing it, and are operating on the assumption the incident was "Islamist-related terrorism."

The assault, which came on the one-year anniversary of the ISIS bomb attacks in Brussels, brought carnage to Westminster, the heart of political life in Britain.

Prime Minister Theresa May described the attack as "sick and depraved." She said attempts to defeat through violence the values Parliament represents would be "doomed to failure."

"The location of this attack was no accident. The terrorist chose to strike at the heart of our capital city, where people of all nationalities, religions and cultures come together to celebrate the values of liberty, democracy and freedom of speech," she said.

Parliament was placed on lockdown for several hours and lawmakers were forced to remain in the main debating chamber of the House of Commons as officers rushed to the scene outside.

Pictures showed scenes of carnage in the aftermath of the attack, which happened as Parliament was in session. One member of the British government gave mouth-to-mouth resuscitation to the officer who died from stab wounds.

"This is a day that we had planned for -- that we all hoped would never happen -- but sadly it is now a reality," said Rowley, acting deputy commissioner of the Metropolitan Police.

He said Palmer, 48, was a father and a husband.

Rowley said 40 people were hurt.