A court in Myanmar has found a prominent filmmaker guilty of defaming the military with his postings on Facebook and sentenced him to a year in prison.

The lawyer defending Min Htin Ko Ko Gyi said he was prosecuted because his posts criticizing the army allegedly threatened to cause members of the military to mutiny or neglect their duties, an offense punishable by up to two years in prison. The filmmaker has been jailed since April.

"Everyone is worrying because I have received one year in jail, but I want to say, don't worry because I will return from prison, and I will continue my work," the defiant filmmaker said.

London-based Amnesty International called Thursday's verdict by the Insein Township Court "an appalling indictment of the state of freedom of expression" and said the punishment was especially cruel because Min Htin Ko Ko Gyi suffers from serious health problems, including liver cancer. It called for his immediate and unconditional release.

"The Myanmar authorities continue to arbitrarily arrest, detain and prosecute activists and human rights defenders simply for peacefully exercising their right to freedom of expression," the human rights group said, calling for an end to laws restricting and criminalizing the exercise of freedom of expression.

Min Htin Ko Ko Gyi's lawyer, Robert San Aung, expressed concern for his client's health in prison and said they will appeal the ruling.

Myanmar ended five decades of military-dominated government in 2016, when an elected civilian government led by Aung San Suu Kyi took office. However, constitutional provisions adopted under military rule ensure the army a major role in government, and initial liberalization of restrictive press laws did not end official efforts to stymie free speech, with reporters and activists continuing to face legal challenges under laws covering defamation and online activities.

PEN America said in a statement the case was another blow to freedom expression in Myanmar and showed the growing lengths to which it would go to silence dissent.

"Ko Ko Gyi's conviction is one more iteration of larger, calculated crackdown by the Burmese government against artists, journalists, activists, and any other cultural practitioners whose ideas pose a threat to those in power," said Julie Trébault, director of the Artists at Risk Connection at the free-expression advocacy group.