BANGKOK – Thailand’s film censors have banned a documentary about the country’s long-running border dispute with neighbouring Cambodia as a threat to national security, the filmmaker said Wednesday.

“Boundary” tells the story of the Thai-Cambodian conflict through accounts of an ex-soldier who lives near the border, as well as villagers from the two countries. It also touches on other conflicts in Thailand, including the 9-year-old insurgency in the south and the political divisiveness that led to a deadly military crackdown on protesters in 2010.

Director Nontawat Numbenchapol said the Culture Ministry’s film screening office informed him that the movie’s content “is a threat to national security and international relations.” He said he will appeal the ban.

The border dispute has its roots in a 1962 International Court of Justice ruling that the 1,000-year-old Preah Vihear temple stands in Cambodia. Thailand’s government argues that definitive boundaries have never been drawn in the area around the World Heritage-listed site.

The dispute has become a rallying point for many Thai nationalists, who don’t recognize the court’s ruling and say the area, including the temple, belongs to Thailand and they have pressured politicians to keep pressing the issue.

The Thai and Cambodian armies have repeatedly clashed in the disputed area in recent years, including in April 2011, when 17 soldiers and a civilian were killed and thousands near the temple were displaced.

In 2011, the court in The Hague created a demilitarized zone around the temple but troops were not withdrawn until a year later.

The court is currently hearing testimony from both sides after they asked it to clarify its original ruling.

According to Nontawat, the film and video screening subcommittee said some of the claims in the documentary, including accounts from the Cambodian side, were “groundless.”

The censors also said some information presented in the film was still being deliberated by the court and had yet to be formally resolved.

Nontawat said he was stunned by the decision.

“I made this movie to create the space for people living near the border to speak their mind,” he said. “Now I have to work harder not only to let people know about the border issue, but also about freedom of expression.”

Thailand’s censors target a wide range of political and social issues. They blur out cigarettes and alcohol on television and crack down on any perceived criticism of the monarchy.

Last year, the film board banned a Thai adaptation of Shakespeare’s “Macbeth,” saying it has content that causes divisiveness among the people. In 2011, the board also banned a movie called “Insects in the Backyard” about a transgender father struggling to raise two children, citing scenes it deemed immoral and pornographic.

“In the U.S., a movie like ‘Bowling for Columbine,’ which boldly criticized the president, can still be shown. It sparked constructive arguments and made the country more developed,” Nontawat said. “In Thailand, the more you censor things, the more you make the country more outdated.”

“Boundary” premiered at the Berlin International Film Festival in February and received financial support from international movie funds.