Police in India have arrested more than 1,100 people following protests against a Bollywood film.
They were prompted by comments from its star, Shah Rukh Khan, regretting that no Pakistan cricketers were picked for next month's IPL cricket tournament.
Hindu hardline party Shiv Sena reacted angrily, vowing to disrupt screenings of My Name is Khan, due out on Friday.
Two small cinemas were attacked in Mumbai (Bombay) and posters burned, prompting police to tighten security.
Authorities have announced that 21,000 police officers will guard the 63 cinemas screening the film in Mumbai, frisking patrons before entering.
Shah Rukh Khan
Shah Rukh Khan was in London last week promoting the film
More security will be provided if needed, said senior police official Himanshu Roy.
Despite the promises of protection, a number of cinema chains have now stopped taking advance bookings for My Name is Khan as uncertainty persists about how effective the security measures will be.
Khan, part-owner of Indian Premier League cricket team Kolkata Knight Riders, spoke out last month after no players from Pakistan were selected for the IPL Twenty20 competition.
The 44-year-old has stood firm over his remarks, but apologised to his My Name is Khan collaborators.
"I request everybody to leave the film alone and deal with what I have said as an individual," he told reporters in London last week.
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In the film, Khan plays a Muslim with Asperger's syndrome whose life in the US changes after the 11 September attacks.
Shiv Sena, a regional party which backs the cause of local Hindus in Maharashtra state, has pledged to continue its protests.
The organisation, often described as anti-Muslim, regards itself as a defender of what it sees as traditional Hindu moral values.
Shah Rukh Khan is one of the biggest stars of India's film industry and has hosted the local version of Who Wants to be a Millionaire.
The eight-team IPL Twenty20 competition starts on 12 March and is staged over 45 days.