Human rights group Amnesty International on Tuesday condemned a Malaysian government ban on Christians using "Allah" to refer to God as "an abuse against free speech".
The Catholic Church in the Muslim-majority country on Monday lost a long-running court battle for the right to use the Arabic word in the local Malay-language edition of its Herald newspaper.
The government has said the top court's verdict pertains only to the paper and Malay-speaking Christians can continue to use "Allah" in their worship.
But lawyers have expressed fears that the ruling will set a precedent to curtail religious minorities' freedom amid what many see as a rise in Islamisation.
London-based Amnesty International said in a statement that the "Allah" ban should be scrapped.
"Malaysia's ban on Christians using the word 'Allah' to refer to God is an abuse against free speech," the group said in a statement.
"The idea that non-Muslims could face prosecution for using a particular word is deeply disturbing," said Amnesty's Malaysia researcher Hazel Galang-Folli.
"This ban... risks further inflaming religious tensions in Malaysia by denying its people the right to freedom of religion."
The dispute over "Allah" began in 2007 when Malaysia's home ministry threatened to revoke the Herald's publishing permit for using the word.
The Church launched a court case, arguing that "Allah" had been used for centuries in Malay-language Bibles and other literature.
But authorities say this could confuse Muslims and entice them to convert -- a crime in Malaysia.
In a statement after the Federal Court verdict, which upheld a lower court's decision in favour of the ban, a government spokesman clarified that Christians "can still use the word 'Allah' in church".
But Christians have expressed their deep disappointment, while Church lawyers have said they will explore ways to further challenge the ban.
Malaysian Bar Council official Firdaus Husni said Christians' concerns were "not without basis" even though "strictly speaking" the verdict applied only to the Herald.
"However, the impact of the decision goes beyond just the publication... It is also likely that the authorities will take further action to curtail the practice of other religions," she told AFP.
About two-thirds of Malaysia's 28 million people are Muslim compared with around 2.6 million Christians.
The multi-ethnic Southeast Asian nation has largely avoided overt religious conflict in recent decades, but tensions have been growing.
In the course of the court case, several churches have been attacked, mostly with petrol bombs causing minor damage, along with some mosques and temples.