Prime Minister Sheikh Hasina on Sunday called for calm after at least four people were killed when police fired on thousands of Bangladeshi Muslims protesting Facebook messages that allegedly defamed the Prophet Mohammed.
Mob attacks over online posts perceived to be blasphemous have emerged as a major headache for security forces in Bangladesh, where Muslims make up some 90 percent of the country's 168 million people.
Some 20,000 Muslims demonstrated at a prayer ground in Borhanuddin town on the country's largest island of Bhola to call for the execution of a young Hindu man charged with inciting religious tension through online messages.
Police said they opened fire in self-defence after some of the crowd threw rocks at officers.
"At least four people were killed and up to 50 people were injured," police inspector Salahuddin Mia told AFP.
He said extra police and border guards were rushed to the island on helicopters and deployed.
The death toll is expected to rise, with local doctor Tayebur Rahman telling AFP at least seven of the 43 people taken to hospital were fighting for their lives.
Prime Minister Hasina said the Facebook account of the man charged with inciting religious tension was hacked by a Muslim person and used to "spread lies".
"We saw rumours are being spread in Facebook to create an environment of anarchy. Who are they? What is their intention?," Hasina said in a speech to her political party's members.
"I asked our countrymen to have patience. And those who want to fish in troubled waters, we will find them and take action against them."
Bhola's deputy police chief Sheikh Sabbir told AFP the man came to the police station on Saturday, claiming his Facebook account was hacked.
"We also suspect that his account was hacked and these contents were spread through Facebook messenger," he said. However, the charges have not been dropped.
In 2016, angry Muslims attacked Hindu temples in an eastern town over a Facebook post that allegedly mocked one of Islam's holiest sites.
In 2012, Muslim mobs torched Buddhist monasteries, houses and shops in the coastal Cox's Bazar district following a Buddhist youth's alleged defamatory photo post of the Koran.
Bangladesh has also experienced a number of attacks on people from religious minorities, secular bloggers, publishers, writers and foreigners, many claimed by Islamist militants.