A woman in Muslim-majority Indonesia was sentenced to 18 months in jail Tuesday for complaining about the volume of a mosque's call to prayer -- the latest conviction under a controversial blasphemy law. Meiliana, 44, an ethnic Chinese Buddhist, was found guilty of insulting Islam for asking her neighbourhood mosque to lower its sound system because it was too loud and "hurt" her ears. There are some 800,000 mosques across the archipelago, with the five-times-a-day call to prayer heard everywhere in the biggest cities and smallest towns. Tuesday's verdict will likely fuel fears that Indonesia's moderate brand of Islam is coming under threat from increasingly influential radicals. The court in the city of Medan on Sumatra island said the woman's comments two years ago triggered riots that saw angry Muslim mobs ransack Buddhist temples. Some ethnic Chinese in the area fled in fear. The defendant's lawyer said his client would appeal the decision while Amnesty International urged a higher court to quash the sentence. "This ludicrous decision is a flagrant violation of freedom of expression," said its Indonesia executive director Usman Hamid in a statement. "Sentencing someone to 18 months in prison for something so trivial is a stark illustration of the increasingly arbitrary and repressive application of the blasphemy law in the country." Indonesia, which has the world's biggest Muslim population, is officially pluralist with six major religions recognised, including Hinduism, Christianity and Buddhism. Freedom of expression is supposed to be guaranteed by law. But criticising religion -- particularly Islam, which is followed by nearly 90 percent of Indonesia's 260 million citizens -- can land offenders in jail. Rights groups have long campaigned against the nation's blasphemy laws, which they say are frequently misused to target minorities. Last year Jakarta's former governor -- the city's first Christian leader of Chinese descent -- was sentenced to two years in jail for blasphemy. Vice President Jusuf Kalla made a plea in 2015 for places of worship to turn down the volume slightly to placate nearby residents.