Thousands of Indians have signed up to an online campaign aiming to clean Facebook of content they consider offensive, raising fears they are trying to "morally police" the social networking site.

Ravi Ghate, a social entrepreneur in the western city of Pune, set up the "Social Peace Force" group on Facebook a week ago following riots in the area, sparked by controversial photos of local leaders posted on the website.

Since then more than 15,000 people have joined the group, whose plan is to click the "report spam" button en masse when they see a post they deem offensive, in a bid to force Facebook to take it down.

"I was thinking, how can we tackle this problem... We must have some method to stop it on Facebook, at the source," Ghate told AFP.

He said the group would only target religious posts that could provoke riots, not political ones.