LONDON (AP) — The Latest on reports of an incident outside Britain's parliament (all times local):

The head of counterterrorism at London's Metropolitan Police says four people have died in the terror incident in London, including an attacker and a police officer.

Mark Rowley says some 20 people have been wounded and Parliament was locked down. A search is underway to make certain no other attackers are in the area — though police believe there was only one attacker.

Rowley said the dead policeman was one of the armed officers who guard Parliament. The other victims were on Westminster Bridge.

Rowley says "We are satisfied at this stage that it looks like there was only one attacker. But it would be foolish to be overconfident early on."

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5 p.m.

The London Ambulance Service says it has treated at least 10 injured people on Westminster Bridge after a vehicle hit pedestrians.

It says the first ambulance arrived within six minutes of the first call at 2:40 p.m. (1440GMT).

Ambulances, an air ambulance and a Hazardous Area Response Team were all sent to the scene.

One woman has been confirmed dead, and a body was seen lying in the yard of Parliament, where a knifeman stabbed a police officer and was shot by police.

People began leaving the Houses of Parliament about two hours after the incident.

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4:50 p.m.

A senior police commander says the attack at London's Parliament has been declared a terrorist incident and "a full counterterrorism investigation is underway."

Commander B.J. Harrington says "a number" of people have been injured, including police officers.

He says additional police officers, armed and unarmed, will be deployed across London during the evening rush hour as part of efforts to keep people safe.

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4:35 p.m.

The Scottish Parliament in Edinburgh suspended its debate on a second independence referendum after the incident outside the British Parliament in London.

Scottish lawmakers had been planning to vote after two days of debate on First Minister Nicola Sturgeon's call for another referendum on leaving the United Kingdom.

The debate was suspended after some members said it should be halted out of respect after a policeman was stabbed and his attacker shot in London.

Sturgeon tweeted that her thoughts were with everyone in Westminster "caught up in this dreadful incident."

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4:30 p.m.

A doctor says a woman has died and about a dozen people are hurt, some with "catastrophic" injuries, after a vehicle apparently hit pedestrians on Westminster Bridge, near Parliament.

Colleen Anderson of St Thomas' Hospital says a female pedestrian has died.

Anderson said: "There were people across the bridge. There were some with minor injuries, some catastrophic. Some had injuries they could walk away from or who have life-changing injuries."

She said there might be a dozen injured in all.

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4:20 p.m.

Poland's former foreign minister, Radek Sikorski, says he was in a taxi leaving Westminster and was checking his email when he heard something like a car crash, "something like a car hitting metal sheet."

"I look up and I see that a person is lying on the pavement. I started my camera and I saw more people lying on the street and on the pavement," Sikorski said on Poland's TVN24.

"People started running up to them. I saw one person who gave no sign of life, another man was bleeding from his head. In all, I saw five people who were at least seriously injured," he said.

"The taxi driver immediately called the emergency number. I heard ambulances within two or three minutes, so the rescue action was really very quick. There is a hospital near there."

"It all happened so fast that there was no time to get scared," said Sikorski who posted his video on Twitter.

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4:05 p.m.

The U.S. State Department says it is closely monitoring the incident outside London's Parliament and urged Americans in London to avoid the area.

Spokesman Mark Toner said Wednesday: "We stand ready to assist in any way the U.K. authorities would find helpful."

He added that the U.S. Embassy in London is closely following the news and stands ready to help any affected Americans.

He said: "Our hearts go out to those affected."

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3:50 p.m.

Witness Rick Longley told the Press Association that he saw a man stab a policeman outside Britain's Parliament.

"We were just walking up to the station and there was a loud bang and a guy, someone, crashed a car and took some pedestrians out," he said.

"They were just laying there and then the whole crowd just surged around the corner by the gates just opposite Big Ben.

"A guy came past my right shoulder with a big knife and just started plunging it into the policeman.

"I have never seen anything like that. I just can't believe what I just saw."

Lawmaker Adam Holloway told the AP he saw people running and immediately ran into his offices in Parliament to be with his staff. "A lot of us are locked in with our staff at the moment," he said.

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3:50 p.m.

The White House says U.S. President Donald Trump has been briefed on a gun and knife incident at Britain's Parliament in London.

Trump himself said during a brief appearance Wednesday before reporters at the White House that he was just getting the news. He called it "big news."

Trump's spokesman, Sean Spicer, says the U.S. will continue to monitor the situation and update the president.

Britain's Parliament was on lockdown after — according to officials — an assailant stabbed an officer then was shot by police.

London Police also said officers were called to an incident on nearby Westminster Bridge

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3:40 p.m.

British lawmaker Grant Shapps said on Twitter that he was walking through the cloisters of the House of Commons to vote when he heard four gunshots. Police told lawmakers to get down on the ground and crawl to cover.

"Police response instant. Heard commotion, looked round. Police weapons drawn, 4 shots, police ordered us to hit ground & get back, get back," he said.

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3:40 p.m.

The former Polish foreign minister Radek Sikorski posted a video on Twitter that seems to show people lying injured in the road on Westminster Bridge.

Sikorski, a senior fellow at the Harvard Centre for European Studies, says he saw at least five people lying on the ground after being "mown down" by a car.

Sikorski told the BBC he "heard what I thought what I thought was just a collision and then I looked through the window of the taxi and someone down, obviously in great distress.

"Then I saw a second person down, and I started filming, then I saw three more people down, one of them bleeding profusely."

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3:35 p.m.

London police say they are treating a gun and knife incident at Britain's Parliament "as a terrorist incident until we know otherwise."

The Metropolitan Police says in a statement that the incident is ongoing. It is urging people to stay away from the area.

Officials say a man with a knife attacked a police officer at Parliament and was shot by officers.

There are also reports of a vehicle hitting pedestrians on nearby Westminster Bridge.

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3:25 p.m.

A European security official says there was increased chatter on jihadi networks Tuesday following the UK's adoption of an electronics ban aboard flights from certain mostly Muslim countries.

He said, however, there was no information that the incident was terror-related.

The official spoke on condition of anonymity because he was not authorized to speak about ongoing security operations.

—By Paisley Dodds.

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3:15 p.m.

The leader of Britain's House of Commons says a man attacked a police officer at Parliament and has been shot by police.

David Lidington says the Parliament complex is in lockdown.

He says there are reports of further violent incidents neaby, and police say they have been called to a firearms incident on nearby Westminster Bridge.

Witnesses said a vehicle struck several people on the bridge, and photos showed a car plowed into railings.

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3:05 p.m.

The leader of Britain's House of Commons says a man has been shot by police at Parliament. David Lidington also said there were "reports of further violent incidents in the vicinity."

London's police said officers had been called to a firearms incident on Westminster Bridge, near the parliament.

A session of Parliament was suspended after the incident.

Britain's MI5 says it is too early to say if the incident is terror-related.

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2:55 p.m.

A session of Britain's House of Commons has been suspended as witnesses reported hearing sounds like gunfire nearby.

The Commons' speaker suspended the session as police responded to an incident.

Journalists at the Parliament building said they were told to stay in their offices.

The Press Association news agency reported that two people were seen lying within the grounds of Parliament.

Police had no immediate confirmation.

Copyright 2017 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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