Hundreds of Bangladeshi activists staged a fourth day of protests Monday over the death of a writer in detention as the UN rights chief called for a review of a digital security law used against opposition figures.

Students tried to march to the home ministry in Dhaka demanding action over what they called the "murder" of Mushtaq Ahmed in a high-security jail, as well as the repeal of the Digital Security Act (DSA).

Riot police stopped them 100 metres from the government complex that houses all major ministries.

Ahmed, one of hundreds detained under the DSA since it was enacted in 2018, died last Thursday at a jail where he had been held since May.

The protesters also demanded the release of more than a dozen activists detained during clashes with police since the death.

Student leader Masud Rana said there could be a "revolt" against the government.

More groups also planned protests during the day over the death of Ahmed, and to demand the release of cartoonist Ahmed Kabir Kishore, who was detained with the writer.

UN High Commissioner for Human Rights Michelle Bachelet on Monday urged Bangladesh to ensure a transparent probe into Ahmed's death.

"There needs to be an overhaul of the Digital Security Act under which Ahmed was charged -- and all those detained under this act for exercising their rights to freedom of expression and opinion must be released," she said in a statement.

Ahmed was detained for publishing an article and sharing Facebook posts critical of Prime Minister Sheikh Hasina's handling of the coronavirus pandemic.

Bachelet also expressed "serious concern" at allegations that Kishore has been subjected "to torture or other ill treatment".

"The government must ensure that its investigation into Ahmed's death is prompt, transparent and independent, and that any allegations of ill-treatment of other detainees are also immediately investigated," Bachelet said.

The country's high court has put off until Wednesday a decision on whether Kishore should get bail, his representatives said.

sam-sa/tw