An upset Aamir at a press meet in Kolkata and in Noida, trained his guns on Bhagat accusing him of being hungry for publicity after the author pointed fingers at the star and the makers of the blockbuster for not giving him due credit.
Aamir accused Bhagat of trying to take away the credit from the film's scriptwriter Abhijat Joshi, who the star said was working on the script for three years.
He also said publicity-seeking people were trying to generate a controversy.
In his response, Bhagat called Khan and the filmmakers -- producer Vidhu Vinod Chopra and Director Rajkumar Hirani -- as 'uncivilised people' and rejected allegations that he was hankering for publicity.
"They are making a fool of themselves," he said. The press meet of the film crew in Noida turned ugly when their reaction was sought on Bhagat's allegation against them.
Chopra lost his cool when a journalist said the film was similar to the book. When Chopra asked that journalist whether he has read the book, he replied in negative after which the producer asked him to shut up.
Aamir also inquired from the journalist whether he had read the book. When Chopra's outbursts were strongly objected to the assembled media, Aamir asked him to apologise but the producer refused
An angry Chopra said, "Aamir had asked me to take the legal course before but now after all this furore I am really angry and I might take a legal action."
"We have signed a very defined contract with Chetan stating his name would appear in the rolling credits of the film. We are going to upload the agreement on vidhuvinodchopra website," Chopra said.
"Chetan is the only person with whom I signed a contract. I had told Raju (director) earlier that this guy is going to create problems later," he added.
Hirani, who has previously directed films like 'Munnabhai MBBS' and 'Lage Raho Munnabhai' for Chopra's banner also tried to pacify the media.
"I want you to recount each and every scene with me from the beginning till the climax and tell me where is it similar to the book (Five Point Someone). There are so many scenes which have nothing to do with the book. I would be very honest that the film has only five per cent of the book and Chetan had read the script and approved of it," Hirani said.
Aamir said that he was told by Chopra and Hirani not to comment on the issue but he felt 'hurt' that 'Hirani's credibility is being questioned.'
"I have nothing to do with this issue. I am the non-interested party but I know Hirani and Abhijat both very closely and I have seen them slogging on the script for last three years. This guy (Hirani) has made Munnabhai films. How can you question him without knowing the whole story?" Aamir said.
Earlier Chetan Bhagat, the author of the book from which the movie has been adapted, accusing the filmmakers and actor Aamir Khan of not giving him due credit.
Bhagat said that 70 per cent of the film '3 Idiots' is based on his novel 'Five Point Someone', contradicting Aamir's claim that he was trying to take away the credit from the film's scriptwriter, Abhijat Joshi.
"From the very beginning the film has been promoted on the lines that it is based on 'Five Point Someone' but when I saw the film, I found out that my name was nowhere to be seen in the credit line," Chetan Bhagat told PTI.
Aamir, who plays the lead in the Rajkumar Hirani directed film, had said, "Abhijat has written the script and Raju Hirani worked on it. Raju and Abhijat took the idea from Chetan's book. The starting point is 'Five Point Someone', but after that the script has been completely changed."
But Bhagat has a different take on it, saying that the credit for the story has been given to Abhijat and Hirani while he has been left out entirely.
"For the past two years I have trusted Hirani, Vidhu Vinod Chopra and Aamir blindly and this is what I get in return. Now I am being threatened with legal action but I am ready for it," Bhagat said.