Police had said earlier that the cause of the collision was under investigation.
Police said 11 people were injured when a auto apparently mounted the pavement and hit pedestrians. The injuries are not considered life-threatening, police said.
One person has been arrested following the accident who has not yet been charged with any offence. Masood acted alone, police said, but may have been inspired by ISIS.
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Massive crowds of families with young children were seen evacuating museums along Exhibition Road following the incident, as authorities cordoned off the area.
The UK is now under a "severe" level of threat of terror attack, according to the MI5 Security Service's rating system.
UK Prime Minister Theresa May was being updated on the incident, her office informed.
He is now in custody at a London police station.
Police are labeling it an "incident" and said they will release more information "when we can". That explosion killed at least six fire service personnel at the scene, and injured at least other 80 people, according to Ghana's state news agency.
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The incident which occurred at 2.20pm immediately sparked a full-scale security lockdown in the area but police later confirmed the collision was not terror-related.
London Mayor Sadiq Khan also tweeted soon after the incident yesterday: "For Londoners and visitors planning to visit our excellent museums and attractions in the area, please be assured they will be open as usual tomorrow [Sunday]".
The police confirmed the incident while noting that the driver of the auto had already been arrested.
Vehicles have been used in a number of attacks throughout Europe in recent years. "My thoughts are with those injured and our thanks to the emergency services".
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