Hundreds of students of Rajshahi University staged impromptu protests, marching on the campus in batches and shouting slogans, demanding the arrest of the killers of English professor Rezaul Karim Siddique, 58.

Siddique was hacked from behind with machetes on Saturday as he walked to the bus station from his home in the country's northwestern city, said local police chief Humayun Kabir.

‘The students were shocked at the latest brutal killing of their teachers. Some 500 of them shouted slogans and joined the marches calling for protection of all teachers and exemplary punishment for the killers,’ said Mostafiz Mishu, a student who witnessed the protests, reports AFP.

Police said Siddique was the fourth professor from Rajshahi University to have been murdered. In February, a court handed down life sentences to two Islamist militants for the murder of another professor, Mohammad Yunus.

The recent killings have sparked outrage at home and abroad, with international rights groups demanding that the secular government protect freedom of speech in the Muslim-majority country.

Ansar al-Islam, a Bangladesh branch of Al-Qaeda in the Indian Subcontinent, this month claimed responsibility for the murder of 26-year-old Nazimuddin Samad, a law student who was killed on the streets of Dhaka, according to US monitoring group SITE.

Police, however, blamed the Ansarullah for the murder.

Bangladesh authorities have consistently denied that international Islamist networks such as Al-Qaeda or the Islamic State group, which recently claimed responsibility for the murders of minorities and foreigners, are active in the country.

A long-running political crisis in the majority Sunni Muslim but officially secular country has radicalised opponents of the government and analysts say Islamist extremists pose a growing danger.