Calcutta: Secularists were back on Shahbag square in Dhaka on Sunday afternoon demanding action against Islamist forces behind Saturday's daylight attack on Muhammad Zafar Iqbal, a science fiction author, physicist, professor and activist, on a day Prime Minister Sheikh Hasina called the attackers "fanatics" who will "suffer in hell".

Iqbal, popular among children for his easy-to-read science fiction - was stabbed in his head and neck thrice during a seminar at Shahjalal University of Science and Technology in the northern city of Sylhet. The condition of Iqbal, who heads the electronics and electrical engineering department, was stated to be stable on Sunday evening.

The stabbing of Iqbal, who was on the hit list of Islamist outfits for his secular views, enraged the country that has witnessed at least 50 attacks, many fatal, on secularists, bloggers, atheists, writers and free thinkers since 2013.

"Why would such attacks continue in our country?" asked Imran H. Sarker of Ganojagoron Mancha, which was at the centre of the protests that rocked the country in February 2013 demanding capital punishment for those convicted of crimes committed during Bangladesh's nine-month war of independence in 1971.

"There have been such attacks in the past and some people have been arrested.... But we need to know about their sponsors and patrons and we demand strongest action against them," he said at Shahbag square, where thousands gathered to express solidarity with Iqbal.

Students had caught the attacker, who has been identified as Foyzur Rahman. Some Bangladeshi newspapers reported that he told interrogators that he attacked Iqbal as he was "anti-Islam".

Iqbal, son of a freedom fighter, and his family have had a huge following in Bangladesh. His elder brother was the legendary author and filmmaker Humayun Ahmed while his younger brother, Ahsan Habib, is a renowned satirist and cartoonist. His admirers posted on social media how a bleeding Iqbal had requested from the hospital bed "not to hurt the attacker" and verify whether he was his student.

"That's the greatness of a man like Iqbal sir," said Riton Das, a Chittagong resident, before attributing his teenager son's success in mathematics Olympiad to Iqbal.

Prime Minister Hasina, whose air ambulance was used to take Iqbal from Sylhet to Dhaka, said: "Those who are committing these crimes are fanatics.... They think by killing a person they will go to heaven, but they will never be able to reach heaven.... They'll suffer in hell."

Monirul Islam, who heads the counter-terrorism and trans-national crime unit of Bangladesh Police, said initially, it was seen as a lone-wolf attack. "But now it seems, Ansarul Islam, popularly known as Ansarulla Bangla Team (ABT), is behind the attack.... We hope to get all the details soon," he added.

The attack has resurrected fears. "The incident reminds us that none of us is safe.... We can be attacked anytime," said the chief editor of a television channel, whose name features prominently on the hit-list of the ABT.

Bangladesh Police sources said that they had been trying to neutralise the ABT through relentless raids on their hideouts and active gathering of intelligence. "But this is a battle that cannot be won only with policing.... The zealots and their ideas for an Islamist Bangladesh need to be crushed, which has to be done by the society," said the journalist.

"If I am quoted by name, they would again be reminded of me," he added, the comment capturing the uncertainty Saturday's attack has injected back into Bangladesh.