Police have arrested more than 11,000 people in the past week, including 194 alleged militants, in a bid to quash a spate of brutal murders of secular writers, gay rights activists and religious minorities.
However, several leading rights experts said that many of the arrests were arbitrary or being used as a way to silence political opponents of the government.
"The government is harassing general people and in some cases, opposition party men, in the name of an anti-militant crackdown," a Bangladeshi university professor and human rights expert told AFP on condition of anonymity.
Human Rights Watch said that while authorities should investigate the crimes and prosecute the perpetrators, the week-long crackdown had seen many people arrested without evidence.
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"After a slow and complacent response to these horrific attacks, Bangladesh's security forces are falling back on old habits and rounding up the 'usual suspects' instead of doing the hard work of carrying out proper investigations," said Brad Adams, Asia director of HRW, in a statement.
He said authorities "should immediately stop arbitrarily arresting people without proper evidence of a crime."
Dhaka has 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.
Police stopped releasing the official number of people arrested after the fourth day of the week-long crackdown following widespread criticism.
The mass arrests expose "the inefficiency of the law enforcers to deal with crimes like these," counterterrorism expert Shahab Enam Khan told AFP.
Hasina accuses the main opposition Bangladesh Nationalist Party and its Islamist party ally, Jamaat-e-Islami, of orchestrating the killings to destabilise the country.
Her government firmly rejects claims of responsibility by the Islamic State group and Al-Qaeda for many murders, saying international jihadist groups have no presence in the country.
The officer had led several high-profile operations against banned militant group Jamayetul Mujahideen Bangladesh, several members of which were arrested in the latest sweep.
In what they called an "important breakthrough", police said yesterday they had arrested a 20-year-old Islamist militant belonging to another domestic outfit suspected of several attacks.
Police said that arrest of Suman Hossain Patowari over an attack on a publisher in October was key to smashing the leadership of the banned Ansarullah Bangla Team.