Bangladesh police have arrested a suspected Islamic militant over the hacking to death of two gay rights activists, part of a spate of murders of intellectuals, writers and religious minorities, officers said on Sunday.

Xulhaz Mannan, editor of a magazine for Bangladesh's gay and lesbian community, and fellow activist Mahbub Tonoy were murdered in a Dhaka apartment last month by about six men carrying machetes and guns.

Police have arrested Shariful Islam Shihab, who they said was a member of a local Islamist militant outfit that has been blamed for a string of similar gruesome murders of secular and atheist bloggers.

"We've arrested one man in connection with the murder of Xulhaz Mannan," Dhaka police spokesman Maruf Hossain Sorder told AFP.

"He is a member of the Ansarullah Bangla Team."

At a press briefing in the capital, police said Shihab - who has denied carrying out the killings - owned one of two guns that were used in the murders.

The 37-year-old was arrested on Saturday in the western town of Kushtia, after raids on several properties, in what Dhaka counter-terrorism chief Monirul Islam said was a "breakthrough" in the case.

"They killed the gay rights activists because they were creating confusion about Islam," Islam said, adding that the investigation was ongoing.

Washington has condemned the killings of Tonoy and Mannan, who worked for US government aid organisation USAID. Both men had received threats from Islamists over their championing of gay rights.

The arrest comes after an elderly Buddhist monk was found hacked to death on Saturday in a temple in the southeastern district of Bandarban - the seventh such killing since the start of last month.

Suspected Islamists have been blamed or claimed responsibility for the scores of murders carried out since last year, as fear grips the Muslim-majority nation over the rising violence.

Al-Qaeda in the Indian Subcontinent (AQIS) said it was behind the killings of 35-year-old Mannan and 35-year-old Tonoy, saying the two men had worked to "promote homosexuality" in Bangladesh.

But Bangladesh police chiefs have said their murders bear the hallmarks of local Islamists, while the secular government has blamed the opposition.

Several members of homegrown Ansarullah Bangla Team were convicted last year over the 2013 murder of atheist blogger Ahmed Rajib Haider.

Last year four secular bloggers and a publisher were hacked to death, while Christians, Hindus and Sufi, Ahmadi and Shia Muslims have also been killed since.

No one has yet been convicted over those deaths, despite a number of arrests.

Islamic State has claimed a number of the killings, but authorities insist there is no evidence of the group's presence in Bangladesh.

A long-running political crisis in Bangladesh has radicalised opponents of the government and analysts say Islamist extremists pose a growing danger.