Sri Lanka's prime minister said on Wednesday that Buddhism will remain paramount on the bitterly divided island, seeking to head off protests led by the powerful Buddhist clergy against proposed changes to the constitution.

The government announced plans last January to devolve power to provinces including in areas dominated by the country's ethnic Tamil minority in an effort to address alienation and bury the kind of ethnic tension that led to a 26-year civil war.

But Buddhists who make up 70 percent of Sri Lanka's 21 million people are opposed to any changes in the constitution under which Buddhism is accorded foremost position while allowing people of other faiths to practise.

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Sri Lanka has chosen only Buddhists for the post of president and prime minister since independence from British colonial rule in 1948. Prime Minister Ranil Wickremesinghe said the Buddhist character of the country would not be touched.

"We are in the process of preparing the new constitution ... the president and myself have agreed to maintain the priority given to the Buddhism in the constitution as it is," Wickremesinghe told a group of Buddhist monks in Colombo on Wednesday.

More than 75 prominent monks last week warned the government not to change the constitution or it would face consequences.

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The opposition, led by former president Mahinda Rajapaksa, and Buddhist groups have warned the government of nationwide demonstrations if the government go ahead with changes to the charter.

Some opposition members have alleged that the new constitution had been drafted to please Western nations and to dilute the influence of Buddhism.

More than 100,000 people were killed in the civil war that ended in 2009 in a crushing defeat for the Liberation Tigers of Tamil Eelam fighting for a separate homeland for the Tamils.