Rights groups accuse security forces of unlawfully killing around 2,500 people since Prime Minister Sheikh Hasina came to power in 2009, many of whom were prominent opposition figures.
Hundreds more have been declared missing, with Sweden-based news portal Netra News this month reporting that some have been secretly detained for years in a previously unknown prison near a military base.
“We want immediate release of the detainees from secret detention cells,” said Sanijda Islam, a member of the local Maayer Daak civil society group which represents families of the missing.
“The authorities should stop their denial,” Islam told AFP.
Outgoing UN human rights chief Michelle Bachelet visited Bangladesh this month and urged the government to create an independent agency to investigate claims of enforced disappearances.
But at a rally in the capital Dhaka, hundreds of people carrying photos of their missing relatives urged the UN to conduct its own inquiry.
“We want a strong investigation committee led by the UN,” said Khondoker Ayesha Khatun, whose son was allegedly abducted by security forces in 2016 and has been unseen since.
There was “overwhelming” evidence that authorities were involved in enforced disappearances and Bangladesh should allow a UN investigation, Meenakshi Ganguly of Human Rights Watch said Tuesday.
“The Bangladesh government should stop feigning ignorance and work with the UN to provide urgent answers and effective accountability,” she added.
Last year the United States imposed sanctions on the elite Rapid Action Battalion police unit, along with seven top security officers, over human rights violations.
The government denies the allegations of disappearances and extrajudicial killings, with one minister saying that some of those who went missing in fact fled Bangladesh.