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

Authorities have come under mounting international pressure to end the attacks in which nearly 50 people have been killed over the last three years, many hacked to death with machetes.

Prime Minister Sheikh Hasina vowed at the weekend to catch "each and every killer" and on Monday police spokesman Kamrul Ahsan said 3,245 suspects had been arrested, raising the total to 8,192 since Friday.

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

Deputy inspector general of national police AKM Shahidur Rahman said most of those arrested were criminal suspects with existing warrants against them, rather than suspected militants. "Only a fraction of the people who have been arrested are members of militant groups," he said.

The crackdown comes after five suspected militants were shot dead in gunbattles with police in recent days. It is thought to have been triggered by the murder this month of Mahmuda Begum, wife of a top anti-terror police officer.

The officer had led several high-profile operations against the banned group Jamayetul Mujahideen Bangladesh (JMB), members of which were among those arrested in the latest sweep.

JMB is one of two local groups blamed by the government for most of the recent killings. Authorities reject claims of responsibility by the Islamic State (IS) group and a South Asian branch of Al-Qaeda and say they have no presence in the country.

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

A BNP spokesman said police had detained more than 2,100 of its activists across the country.

"Police have arrested and harassed opposition activists and ordinary people in the name of the crackdown. Also many of our activists have fled their homes, fearing arrests," Rizvi Ahmed told AFP.

"Police have said several suspected militants have been shot dead in crossfire. Instead of putting them into trials, these suspected militants are being eliminated in cold blood."

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.

Bangladesh is officially secular, but around 90 percent of its 160 million-strong population is Muslim.

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

Mubashar Hasan, an expert on political Islam, said the crackdown risked further alienating hardliners who feel they have no choice but to join the militants.

A previous government crackdown on government opponents - including a ban on Jamaat - following a protracted political crisis is widely blamed for pushing many Bangladeshis towards extremism.

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

National police chief Shahidul Hoque defended the crackdown, saying only those suspected of wrongdoing were being picked up.

AFP