RNA - Police say the dead include a police officer and the suspected assailant, as well as two pedestrians who were on Westminster Bridge.
Authorities have declared the attack a "terrorist incident," while also saying in a statement investigators "remain open minded to the motive."
Britain's Press Association reported that a car barreled into pedestrians along the sidewalk of Westminster Bridge, causing multiple "catastrophic injuries." Police said investigators believe this is where the two civilian deaths occurred.
The car then crashed into the fence that surrounds Parliament, and a man armed with a knife emerged and stabbed a police officer. The attacker was later shot and killed by police.
The UK parliament building was under lockdown and MPs were advised to remain inside the building.
David Lidington, the leader of parliament's lower House of Commons told MPs: "What I am able to say to the house is there has been a serious incident.”
"It seems that a police officer has been stabbed, that the alleged assailant was shot by armed police,” he noted, adding, "There are also reports of further violent incidents in the vicinity of the Palace of Westminster."
According to Lidington, an air ambulance was at the scene to take away casualties.
Following the incident, traffic was halted on Westminster Bridge with emergency vehicles swarming the area and police completely shutting off the bridge to traffic.
According to AFP, Westminster station on the London Underground train network, which is opposite the Houses of Parliament, was also closed,
No group or individual has so far assumed responsibility for the incident and a British security source have told Reuters that the motivation of the attack remains unclear.
The Metropolitan Police said that armed officers are among the law enforcement personnel "on scene and dealing with the incident." It said police were called to the scene at around 2:40 pm, local time.
The House of Commons session was suspended and members of parliament who were in the chamber were told to remain there.
Meanwhile, a spokesman for British Prime Minister Theresa May said she was safe but did not specify where the prime minister was during the attack.
The Westminster incident took place on the first anniversary of attacks in the Belgian capital Brussels that left over 30 people dead and more than 300 others injured.
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