Bangladesh authorities should immediately end arbitrary arrests of opposition party members and others, Human Rights Watch (HRW) said.
Arrests have continued even after the ruling Awami League party and its allies won the largely uncontested elections held on January 5, 2014, HRW claimed.
The United States, European Union, and others refused to send observers to Bangladesh's divisive polls.
Hundreds of opposition leaders and members were taken into custody before the elections, which were boycotted by the main opposition alliance led by the Bangladesh Nationalist Party (BNP).
BNP leader and two-time former Prime Minister Khaleda Zia was placed under de facto house arrest, with security forces surrounding her residence and blocking people from entering and leaving.
Asia Director at Human Rights Watch Brad Adams said that the Awami League claims that it is the leading democratic party in Bangladesh, but there is nothing democratic about this kind of widespread crackdown on critics.
Nearly 150 people have been killed in political violence in recent months, much of it carried out by opposition activists, HRW said.
The international community has urged Bangladesh political leadership to initiate dialogue that will end the political violence.
