Metropolitan Police's deputy assistant commissioner Neil Basu said the "terrorist attack" began when the van was driven into a man who was already being given first aid by the public on the pavement.
Image copyrightReutersImage copyrightGetty ImagesImage caption
Police are examining the van used in the attack
The Muslim Council of Britain said this was the "most violent manifestation to date" of recent Islamophobic incidents.
Media captionAbdulrahman Aidroos describes how he and others detained the suspected attackerThis is the fourth terror attack in the UK in four months, after incidents in Westminster, Manchester and on London Bridge.
Image copyrightAFPHome Secretary Amber Rudd described it as an appalling incident, and said new funding for security at religious sites had recently been arranged.
Image copyrightAFPImage copyrightEPALabour's shadow home secretary and Hackney North and Stoke Newington MP Diane Abbott said on Twitter that police "must urgently review security for all mosques".