By Ruma Paul

DHAKA (Reuters) - Authorities in Bangladesh have arrested at least 85 militants as part of a broad crackdown on Islamists after a wave of brutal attacks on minorities and liberal activists, police said on Sunday.

A total of more than 5,000 suspected criminals have been arrested since law enforcement agencies began a week-long drive on Friday to halt a series of targeted killings in the mainly Muslim nation.

All arrests were made on specific charges, national police chief A.K.M. Shahidul Hoque said, relating to firearms, narcotics and other offences.

“We will have to prevent the emergence of militancy collectively as a whole nation,” Hoque said.

In the past week an elderly Hindu priest, a Hindu monastery worker and a Christian shopkeeper were hacked to death in attacks for which Islamic State claimed responsibility. The Muslim wife of a key counter-terrorism police official was also stabbed and shot dead.

Militants have killed more than 30 people in Bangladesh since early last year, with atheist bloggers, liberal academics, gay rights campaigners, foreign aid workers, members of minority Muslim sects and other religious groups among the victims.

Islamic State has claimed responsibility for 21 of the attacks since its first claim in September last year and al Qaeda has claimed most of the rest, according to Site Intelligence Group, a U.S.-based monitoring service.

The government denies that either group has a presence in Bangladesh and says that home-grown radicals are responsible.

Last month junior foreign minister Shahriar Alam told Reuters that Islamic State was trying to ride a wave of religious radicalization by falsely claiming killings and said there was enough evidence implicating domestic militant groups.

Police said that two home-grown militant groups -- Jamaat-ul-Mujahideen and Ansarullah Bangla Team -- were behind the attacks as part of their campaign to impose strict Islamic law on Bangladesh, whose population of 160 million are mostly moderate Muslims.

At least 10 suspected members of the outlawed Jamaat-ul-Mujahideen were killed in shootouts since November, including five last week, police said.

Prime Minister Sheikh Hasina has vowed to track down the killers, blaming the growing violence on political opponents linked to Islamist parties.

The opposition party, led by former Prime Minister Khaleda Zia, denies the accusations and said that mass arrests were a ploy to suppress political opponents.

(Editing by David Goodman)