UK police on Monday (26) said they were investigating the knife attack on the woman in a London park wearing a T-shirt with a cartoon from Charlie Hebdo, the French magazine targeted by jihadists.
The 39-year-old victim suffered a stab wound and was seen with blood pouring down the side of her face after the stabbing at the site where people gather for public speeches and debates on Sunday, reports said.
She was treated in hospital for a minor slash injury after the attack on Sunday afternoon at Speakers Corner' in Hyde Park, Metropolitan police said.
Footage posted on YouTube showed a man in a hooded top approach a woman holding an umbrella and stab her, apparently several times.
The woman's T-shirt has the Charlie Hebdo logo and a cartoon showing a Muslim man kissing a cartoonist with the slogan "L'amour plus fort que la haine" (love is stronger than hate).
Speakers' Corner is a historic place for open-air debate where people are allowed to make speeches on any lawful subject.
Police has not identified the victim yet but some social media handles claimed that she was Hatun Tash, a preacher from a group called DCCI Ministries that says it seeks to preach the Christian Gospel to Muslims.
Detectives said they had recovered a knife at the scene and the victim has given 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," said Detective Superintendent Alex Bingley.
Bingley asked people not to "speculate on the motive for the attack until we have established the full facts".
Twelve members of staff at the satirical weekly Charlie Hebdo were gunned down in January 2015 by two brothers who vowed allegiance to Al-Qaeda.
Bob Blackman MP speaks during the event