UPDATE: Four dead, 20 injured in attack near British Parliament

LONDON (AP):
A knife-wielding man went on a deadly rampage at the heart of Britain's seat of power Wednesday, mowing down pedestrians on London's Westminster Bridge before stabbing an armed police officer to death inside the gates of Parliament. Four people were killed, including the attacker, and about 20 others were injured.

Lawmakers, lords, staff and visitors were locked down as the man was shot by police within the perimeter of Parliament and just meters from entrances to the building itself.  He died, as did two pedestrians on the bridge, and the police officer.

A doctor who treated the wounded said some had "catastrophic" injuries.

In the House of Commons, deputy Speaker Lindsay Hoyle announced that the sitting was being suspended and told lawmakers not to leave.

Police said they were treating the attacks as a terrorist incident and had launched a full counterterrorism investigation. There was no immediate claim of responsibility.

"We are satisfied at this stage that it looks like there was only one attacker," said Metropolitan Police counterterrorism chief Mark Rowley. "But it would be foolish to be overconfident early on."

The threat level for international terrorism in the UK was already listed at severe, meaning an attack is "highly likely."

IN PHOTO: Armed police officers enter the Houses of Parliament in London, on Wednesday.

Wednesday was the anniversary of suicide bombings in the Brussels airport and subway that killed 32 people, and the latest events echoed recent vehicle attacks in Berlin and Nice, France.

As lawmakers were voting inside Parliament, many reported hearing the sound of gunshots. Parliament was locked down for two hours, and adjoining Westminster subway station was shuttered.

Conservative parliamentarian Tobias Ellwood, whose brother was killed in the Bali terror attack in 2002, performed mouth-to-mouth resuscitation on the police officer who was stabbed and later died. About 10 yards away from the police officer was the attacker who was shot dead by police after scaling the security wall toward the Parliament's grounds.

Ellwood, who served in the British military and served in Bosnia, Northern Ireland, Kuwait and Cyprus, applied pressure to the police officer's multiple lacerations.

Photographs showed Ellwood's bloodied hands and face from the police officer's wounds while the alleged attacker was seen nearby.

Ellwood has been an undersecretary at the Foreign Office since 2014, covering the Middle East and Africa.