Bangladeshi police have arrested at least 20 people for questioning over the murder of a prominent university professor who was hacked to death, several years after he led a push to ban students wearing full-face veils.
The victim, Shafiul Islam, was killed on Saturday near Rajshahi University in the west of the Muslim-majority country where he was a professor of sociology, a senior officer said on Sunday.
The professor followed the folk sect Baul, popular in parts of western Bangladesh, whose members call themselves followers of humanism rather than a particular religion.
The murder has triggered protests in the capital Dhaka and in Rajshahi where mainly students have marched through university campuses and boycotted classes since news of the killing broke on Saturday.
"We are working on several possible motives behind the killing," Rajshahi police commissioner Mahbubur Rahman told the AFP news agency, adding that the "leading" one was that the murder was carried out by an armed group.
He said about 20 people have been arrested but declined to say which religious or political groups they were connected to.
Local newspaper Dhaka Tribune reported that the principal of Islamia College was among those arrested.
A previously unknown group calling itself the Ansar al-Islam Bangladesh-2 claimed responsibility for the killing, after opening a Facebook page late on Saturday.
"Our Mujahideens have today murdered an apostate who had prohibited female students from wearing veils in his department and the classrooms," a posting said."Beware all the anti-Islamic apostates and atheists!"
The Facebook page quoted a local news report from 2010 saying the professor forced female students to remove their veils before entering his classroom.
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Sirajul Islam, also a sociology professor, said the slain teacher was not anti-Islam but was against full-face veils.
"He moved to ban full-face veils from the classrooms and examination halls. He thought full-face veils could be used to cheat in the examinations and it was impossible to identify a student who wears a full-face veil," he told AFP.
Rajshahi University had been a stronghold of the student activist wing of the country's largest Islamist party, Jamaat-e-Islami, before police launched a crackdown on the group, after the secular government of Prime Minister Sheikh Hasina took over in 2009.
Bangladesh is the world's third largest Muslim-majority nation with the vast majority following a moderate form of the religion. A more strict interpretation of Islam has gained strength in recent years, but killings carried out in the name of the religion are rare.
In 2004 a famous writer was attacked and a well-known atheist blogger was killed in February last year by those opposed to their views.
In August, a moderate cleric who hosted popular shows on TV was killed. The same group that was blamed for the atheist blogger's death was accused of his murder.