Six Islamist militants responsible for a series of deadly attacks in Bangladesh, including one behind the brutal killing of a secular publisher last year, have been arrested, police said on Wednesday.

Police said Moinul Islam Shamim, the prime suspect in the murder of publisher Faisal Arefin Dipan, has been arrested.

Shamim has been described as key organiser of Ansar Al Islam, also known as Ansarullah Bangla Team (ABT) which has presumed ideological links to al-Qaeda.

"We arrested him (Shamim) last night from Tongi area (on the outskirts of the capital)," the spokesman said, adding Shamim was the trainer of the assailants of Dipan, who was stabbed dead inside his office at Dhaka’s Shahbagh area on October 31 last year, the day when suspected ABT activists also attacked another publisher leaving him critically wounded.

Rahman said during initial interrogations, Shamim said fugitive key-ABT leader Ziaul Haque was also involved in Dipan’s murder while the banned outfit had targeted him for publishing books of slain Bangladeshi-born US blogger and science writer Avijit Roy.

"But we suspect him (Shamim) to be involved also in the murder of a university student in January this year," the spokesman said.

Roy was hacked to death on the campus of premier Dhaka University on February 26 last year, when he was coming out of an annual book fair while the assailants also attacked his wife, who narrowly survived.

The five others were arrested in overnight raids from different areas of the capital by the elite anti-crime Rapid Action Battalion (RAB), which described them as operatives of Jamaatul Mujahideen Bangladesh (JMB), the outfit is said to be inclined to the ideology of the Islamic State militant group.

ABT is blamed for a series of attacks on individuals, including secular writers and activists, followers of minority religious faiths while independent security analysts believe they are inclined to al-Qaeda.