A mural by urban artist Banksy in Bristol has been daubed with red paint.
A group called Appropriate Media said it painted over the picture, entitled The Mild Mild West, as a protest over the Stokes Croft area being gentrified.
Oli Wells, director of Coexist, which is behind the area's refurbishment, said he did not understand the group's actions.
"We don't see how spraying a much-loved mural will help with positive change for the area," he said.
"I'm confused at the message from whoever did it. We're fully aware of the nature of Stokes Croft being an outdoor gallery and therefore open to all sorts of interpretation and retaliation but we can't understand why they've made the Banksy a target," said Mr Wells.
In a statement on its website, Appropriate Media said: "Graffiti artists are the performing spray-can monkeys for gentrification."
The mural Mild Mild West, which depicts comic policemen and a bear, was voted Bristol's favourite alternative landmark in an online poll in 2007.
Businesses and people living nearby have spent the morning helping to clean the paint from the picture.
"It's been cleaned by the community who sit outside and enjoy the artwork - street drinkers and local businesses working together so it seems to indicate the local community like having the Banksy there," said Mr Wells.
"I'd love to talk to these people and find out what they're interested in and the part they'd like to play in the Stokes Croft area. We have an open door and would welcome their involvement in the project," he added.
Art by guerrilla artist Banksy regularly sells for hundreds of thousands of pounds.
Bristol City Council has estimated the cost of cleaning all the graffiti in Bristol at about £5m.