Dressed in a torn T-shirt, shackled in chains with bruises painted on his body, Khanna posed in an advert with the tagline "Beaten, shackled, abused - elephants do not belong in zoos" for People for the Ethical Treatment of Animals (PETA).

"It's a simple fact. When a celebrity speaks, people listen," said Anuradha Sawhney, chief functionary for PETA India.

"Every time a celebrity speaks out for a cause, be it for animal abuse in circuses, or their conditions in zoos, or the suffering in factory farms, a lot of compassionate people come forward to find out how they can help."

PETA offices get flooded with calls, letters and e-mails from people asking questions or enlisting their help, said Sawhney.

Aishwarya Rai wrote a letter on behalf of PETA to help save an endangered black rhinoceros in South Africa, Shilpa Shetty donned a body-hugging tiger-striped bodysuit urging people to boycott circuses and Madhuri Dixit wrote to the government in support of elephants.

Other stars include actor John Abraham who posed in an open cage saying "Let birds fly free" and dancer Rakhi Sawant who stood for almost five hours to have her body painted in tiger stripes for an anti-circus ad.

PETA's latest campaign, which involves Khanna, is to promote awareness of the treatment of elephants in zoos and cities.

Animal rights activists say elephants are often ill-treated in cities where they are used by their owners to beg, and are poorly fed and forced to walk on tarmac roads day and night.

In zoos, the animals are separated from their families and sentenced to a lifetime of boredom, loneliness and abuse, say activists, adding that elephants are intelligent, sensitive and social creatures which live in closely knit family groups. "These majestic animals belong in the wild, but instead they are locked up like criminals -- even though they've committed no crime," said Khanna.