Dhaka, Bangladesh (CNN) Authorities in Bangladesh have arrested nearly 150 suspected militants and more than 11,000 others as part of a crackdown on extremism after a wave of brutal killings.

Police said they detained 145 suspected Islamist militants over four days of raids and that the rest were accused of everything from theft and drug dealing to violence.

Detained Bangladeshis in a police van prison van as they are taken to the Dhaka Magistracy in Dhaka.

An officially secular but Muslim-majority nation, Bangladesh has seen a surge of targeted killings -- blamed on Islamist radicals -- that have claimed the lives of secularists, religious minorities and gay activists

Police have said that most of the suspected militants were members of Jama'atul Mujahedin Bangladesh, a banned Islamist group.

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.

A man is frisked by Bangladesh police on June 10, 2016.

The JMB also has been blamed for bomb attacks, and members of the group were detained in relation to the recent killing of a Hindu priest.

Last week, the wife of a senior police officer who had led high-profile operations against the group was stabbed and shot to death while taking her to son to catch his school bus.

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.

A man on a motorcycle is stopped at a police check-post in Gulshan in the capital of Dhaka.

"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 (in black veil) waits in front of Dhaka Magistracy to find out where her husband is, after he was detained by city police in Dhaka on Tuesday.

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.