AMNESTY International has launched an investigation into the imprisonment of four Vietnamese officials jailed for helping a Hongkong film company produce a controversial movie in the country. Stars and Roses, starring Andy Lau and Cherrie Chung, grossed $13 million during a three-week Hongkong run in 1989. But it was banned soon after it opened in Hanoi in June 1991 because of scenes of prison torture, re-education camps and a government crackdown on human rights campaigners. Hongkong's Chun Sing Film Company has admitted it added the sensitive footage after returning to the territory, in the wake of sentiment from the June 4 Beijing crackdown. The company has been blacklisted by Vietnam. The movie, also known as Loving the Songs From Vietnam, tells the story of a Hongkong businessman thrown in and out of prison in Vietnam until he is rescued by a woman interpreter who helps him cross the border to China. After it aired in Hanoi, the director-general of the government-run Union of Video Cinematography Enterprises, Pham Cong Canh, who had allowed the 30-strong Hongkong crew into Vietnam, was arrested along with three junior colleagues. Last November, he and Pham Kim Thanh were jailed for three years for''internationally violating state economic management principles, policies and regulations with serious consequences,'' as well as ''causing serious consequences through negligence''. Nguyen Quoc Minh was given two years in prison for negligence under the Vietnamese Criminal Code, while Huyn Xay was jailed for 16 months for the crime of ''anti-socialist propaganda''. Amnesty International's Vietnam researcher, Mr Rolando Medina, said there was ''a very high possibility'' at least one of the four men was a prisoner of conscience. He said: ''It could be that all four are prisoners of conscience because the economic terms could just be a cover.'' The human rights organisation has written to the Vietnamese authorities demanding to know where the four are detained, the reasons for their arrest and the nature of the judicial process. It is awaiting a reply from Hanoi. If Amnesty International establishes the men are prisoners of conscience, it will call for their immediate release. During the trial the government alleged the controversial scenes violated the contract and that Pham Cong Canh and his colleagues allowed Chun Sing to make the film with ''reactionary contents'' in order to smear the country. It claimed it had warned Pham Cong Canh about the subject matter, but he did not try to edit the film before the crew left the country. The four also allegedly accepted only half of the agreed sum of US$80,000 (HK$624,000) to film in the country. According to the government prosecutor, the accused dishonestly used the money and were ''blinded by money and forgot their responsibility towards their country''. Chun Sing director Mr Taylor Wang Siu-ming last week said he felt sorry for the four officials. ''I have done nothing wrong. Whether the film was reactionary in content is subject to different points of view. The film is not about politics. ''If we look at things from a political angle, anything can be interpreted as having political implications.'' Of the controversial footage added later, Mr Wang said: ''There were just a few scenes showing Vietnamese students demonstrating in the streets demanding democracy. ''We did it in the hope of echoing the pro-democracy movement at Tiananmen Square. And the background was set in Vietnam before the reunification.'' The film company was blacklisted after leaving Vietnam and Mr Wang said he would discourage other film-makers in the territory from going there. ''I swear I'll never go back to Vietnam again. It's frustrating filming in communist countries like Vietnam. Places like Thailand and Malaysia are much better,'' he said.