A trailer for the film, directed by Ing Kanjanavanit, shows scenes from Thailand's recent past, including a 1973 crackdown on student protesters and street clashes in 2010 between the military and anti-government demonstrators in which 91 died.

"The film 'Shakespeare Must Die' has content that causes divisiveness among the people of the nation," the Film Censorship Board said in a statement late on Tuesday. "The film is grouped under films that are not allowed to be distributed in the Kingdom."

'Macbeth' is the story of a power-hungry general in ancient Scotland who kills the king for his throne, and commits more murders to hold onto it.

Themes of greed and power could touch a raw nerve among Thais who have been divided since the run-up to a 2006 coup that toppled former premier Thaksin Shinawatra. He is adored by the rural masses, but detested by royalists and Bangkok's elite.

Thaksin and some of his supporters have been accused of republican leanings, charges they deny.

Anything that involves monarchy is a highly sensitive issue in Thailand. Ailing 84-year-old King Bhumibol Adulyadej is regarded as semi-divine and criticism of the monarchy can be met with charges of lese-majeste, which carry up to 15 years in jail.

That does not appear to be the trouble with the film, which was the last one to receive support from a Culture Ministry fund under the previous government of Abhisit Vejjajiva, an opponent of Thaksin.

"I was shocked. I didn't expect this film to be banned," director Ing told Reuters on Wednesday. "Yesterday the censor board asked me if I wanted to change the current political system."

Thaksin's sister Yingluck is now prime minister, but he remains in self-imposed exile, refusing to return if he has to serve jail time for a graft conviction he says was politically motivated.

In Thailand, viewers would be likely to associate Ing's depiction of red-clad protesters with pro-Thaksin supporters known as the "red shirts", who brought central Bangkok to a halt for nine weeks in 2010 before their movement was ended by the military.

Ing defended her use of the color.

"Red is the universal color for killer. In Thai soap operas the bad guys wear red, so why am I not allowed to use it?"

"Did Thaksin affect my life? Absolutely. In this sense the film is a political one but we also wanted to bring Shakespeare to a Thai audience," she said.

"We made a Shakespearean film because we are living through Shakespearean times. People find the truth in fictional form threatening."

(Editing by Alan Raybould and Daniel Magnowski)

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