Salman Khan, known for playing a tough guy in his films, has been branded a "non-believer" and ordered to reaffirm his faith in Islam after participating in a festival honouring Lord Ganesh in Mumbai on Tuesday.

The order came from scholars at the influential Daarul-Ifta Manzare school in northern Uttar Pradesh state, which claims hundreds of thousands of followers among India's approximately 140 million Muslims.

"Be it a pauper or a king, everyone has to follow the dictates of Islam -- nobody has been given the exemption to bypass the tenants of the religion," religious scholar Nafeez Khan told.

The 41-year-old actor must reaffirm his faith before an imam and two witnesses, the cleric said, describing the religious decree as "right and appropriate."