The 39-year-old was taken to hospital after the attack in London’s Hyde Park, police say.
A woman has been slashed with a knife at Speakers’ Corner in London’s Hyde Park, police have said.
The 39-year-old was taken to hospital after the attack on Sunday afternoon at the site, where people gather for public speeches and debates.
The Metropolitan Police said she received a minor slash injury to the head, which was not life-threatening.
Footage shared on social media shows someone dressed in black approaching a woman wearing a Charlie Hebdo T-shirt.
She is later seen clutching her right hand close to her body, with what appears to be blood at her temple, as she is helped into a police van by officers who were nearby.
Charlie Hebdo is a French satirical magazine that was targeted in a deadly attack by Islamist extremists in 2015 after it published a cartoon of the Prophet Mohammed.
Twelve people were killed in the attack at the magazine’s offices in Paris.
A knife was found after the attack in Hyde Park, but no arrests have yet been made.
Officers based in Westminster are working with the specialist Met unit which patrols the royal parks to investigate and try to find the person responsible.
The Met said officers were called just after 15:30 BST to reports that a woman had been assaulted.
A statement said she was treated by the London Ambulance Service before being taken to a central London hospital.
Det Supt Alex Bingley, of the Central West Command Unit which covers policing in Westminster, said: “This was clearly a very distressing incident for the woman involved and officers have spent time with her, whilst she was being treated for her injury, to get an account of what happened.
“We know that this assault was witnessed by a number of people, many of whom captured it on their phones. I would ask them, if they have not already done so, to contact police.
“We remain in the early stages of our investigation and are working hard to trace the person responsible.
“I would ask people not to speculate on the motive for the attack until we have established the full facts.”