A man died and nine other people were taken to hospital following the incident on Seven Sisters Road, which police are treating as a terror attack.
She also said that police declared it a terrorist incident within eight minutes, and that it was "an attack on Muslims near their place of worship".
London Mayor Sadiq Khan urged people to "remain calm and vigilant" and said the Met had deployed extra police to reassure communities, especially those observing Ramadan.
Police were on Monday searching an address in a cul-de-sac close to Cardiff golf club in the northeast of the city suburbs.
Deputy Assistant Commissioner Neil Basu, national counter-terrorism coordinator, said the victims were all from the Muslim community.
The suspect's mother expressed shock at knowing that her son was behind the attack.
"Like the bad attacks in Manchester, Westminster and London Bridge it is also an assault on all our shared values of tolerance, freedom and respect", he said in a statement, referring to attacks in previous months. In 2015, One-time Community Police Officer of the Year, Damian O'Reilly, made a heartfelt appeal to May to reverse cuts to local policing which had caused intelligence about possible attacks to dry up.
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Moments after the driver was captured, Mohammed Mahmoud and others intervened to keep him from being attacked by people enraged by his actions.
Police said at this stage they believe the suspect acted alone.
"By God's grace, we were able to protect him from harm", the imam said.
A man driving a white van mounted a pavement and hit a group of worshippers exiting the mosque just after midnight.
"One eyewitness to the attack told the BBC that the driver of the van reportedly said "'I want to kill Muslims, I want to kill Muslims, '" as he exited the vehicle. Since then incidents of hate crime have risen, police say.
"I've heard stories form the imam who stopped local residents from understandably taking out their anger on this terrorist", Khan said at a press conference.