But the opposition Bangladesh Nationalist Party, or BNP, said the raids were designed to detain its leaders and workers. It said some 2,100 party leaders and activists were arrested.

Police seized arms, ammunition, other lethal weapons and more than 2,000 motorbikes during this week's raids.

Marcia Bernicat, U.S. ambassador to Bangladesh, said there have been at least 35 such attacks carried out over 14 months, with an Islamist terror group claiming responsibility for 23.

'Killers brought to book'

The government has been criticized for not doing more to respond to the killings.

Prime Minister Sheikh Hasina said over the weekend that she wanted to bring all the perpetrators to justice.

"Where will the criminals hide? Each and every killer would be brought to book as we have done after 2015 mayhem," Hasina said.

The Bangladeshi government accuses the opposition BNP and Islamic fundamentalist groups for the attacks.

"All terror in Bangladesh for the last four years, the answer is very simple," Information Minister Hasanul Haq Inu told CNN in a recent interview, pointing to a series of Islamist parties, organizations and jihadist groups.

"The producer is BNP, the director is Jamaat e Islami, and the small actors on the ground are variants of ABT (Ansarullah Bangla Team), JMB, and certain other militant Islamic networks," he said.

No answers

Families of those arrested say they have been kept in the dark over the raids.

Sanjida Begum waited outside the Dhaka Magistracy to ask authorities of the whereabouts of her husband, Iqbal Ahmed, who was detained Monday afternoon.

"I've heard my husband will be brought here today, but I'm yet to see him," Sanjida told CNN, her daughter and a relative by her side.

Iqbal was picked up from the a city bus stand without explanation, she said. "I don't know if he is involved in any kind of criminal activity. He's never been arrested before," she said.