Bangladesh police said Monday they have arrested more than 8,000 people in a nationwide crackdown on militants launched after a series of murders targeting minorities and secular activists.

Prime Minister Sheikh Hasina vowed on Saturday to catch ‘each and every killer’ as Bangladesh reels from a wave of gruesome killings of religious minorities and liberal activists that have spiked in recent weeks.

Police spokesman Kamrul Ahsan said 3,245 suspects had been arrested as part of the anti-militant drive in the last 24 hours, raising the total number to 8,192 since the campaign began Friday.

Bangladeshi authorities have come under mounting international pressure to end the attacks, which have left nearly 50 people dead over the last three years.

But opposition parties have accused the government of using the crackdown to suppress political dissent.

Most of those arrested were suspected ordinary criminals with existing warrants against them, deputy inspector general of police AKM Shahidur Rahman told AFP.

‘Only a fraction of the people who have been arrested are members of Islamist militant groups,’ he said, adding the total number of militants arrested since Friday was 119.

The week-long crackdown is part of ramped up efforts to halt the killings, with five suspected Islamist militants shot dead in gun battles with police in recent days.

Among those arrested in the latest sweep were members of banned group Jamayetul Mujahideen Bangladesh (JMB), police said.

JMB is one of two local groups blamed for most of the recent killings. The government rejects claims of responsibility from the Islamic State (IS) group and a South Asian branch of Al-Qaeda, saying international jihadists have no presence in Bangladesh.

Premier Hasina accuses the main opposition Bangladesh Nationalist Party (BNP) and Islamist party ally, Jamaat-e-Islami, of orchestrating the killings to destabilise the country.

- 'Innocent people' - Omar Faruq, an alleged senior official of banned Islamist outfit Hizb ut Tahrir, was also among those arrested Monday, a local police chief told AFP from the northwestern district of Chapai Nawabganj.

‘We seized anti-government leaflets, pistol and gunpowder from his possession,’ Bashir Ahmed said.

‘Faruk was previously arrested in 2012 and went out on bail. Then he started trying to re-organise the activities of the banned organisation,’ he said.

Mubashar Hasan, an expert on political Islam, said the crackdown has the potential to further alienate and anger hardliners who feel they have no choice but to join the militants.

‘While fighting militants on the ground is important, winning hearts and minds of people is crucial so that more people do not join militancy,’ Hasan, from Dhaka's University of Liberal Arts, told AFP.

Experts say a previous government crackdown on its opponents, including a ban on Jamaat following a protracted political crisis, has already pushed many towards extremism.

A BNP leader on Saturday accused police of detaining ‘many ordinary and innocent people’.

Last week an elderly Hindu priest was found nearly decapitated in a rice field, while a Christian grocer was hacked to death near a church. IS claimed responsibility for those murders as well as that of a 62-year-old Hindu monastery worker on Friday.

Although the country is officially secular, around 90 percent of Bangladesh's 160 million-strong population is Muslim.

Other victims have included liberal activists and secular bloggers along with two foreigners and two gay rights activists.

With concerns raised over the sheer number of arrests, national police chief Shahidul Hoque defended the crackdown, saying only those suspected of wrongdoing were being picked up.

‘They are arresting the persons already facing certain allegations,’ he was quoted in a local newspaper as saying in Chittagong city.