A man arrested outside Buckingham Palace, London, on Friday night was brandishing a 4ft sword as he repeatedly shouted “Allahu Akbar”, police said on Saturday.
Dean Haydon, head of counter-terrorism at Scotland Yard, said the man drove at a police vehicle before stopping and being confronted by three officers.
The incident occurred outside the Mall roundabout near Spur Road – which runs along the corner of the Palace grounds – at about 9pm on Friday.
A man had stopped his car in a “restricted area” and police saw the weapon in the passenger footwell of his car.
BBC reports that CS gas was used to restrain the 26-year-old, from the Luton area, who is now in custody.
The three officers were treated for minor injuries.
Two of them were taken to hospital after receiving cuts to their hands and forearms.
Counter-terror police are investigating after the man was arrested on suspicion of grievous bodily harm and assault, and under the Terrorism Act.
No members of the Royal Family were in Buckingham Palace at the time.