The sentencing of Abdul Quader Mollah by a war crimes tribunal on Tuesday for charges including murder, rape and torture was the second verdict in trials that have reopened the wounds of Bangladesh's struggle to break away from Pakistan.
The popular unrest on Wednesday was compounded by a national strike, organised by Mollah's Jamaat-e-Islami party, which entered its second day. About 50 people were injured and about 100 arrested in clashes between Jamaat activists and police.
Troops patrolled government buildings and intersections in the capital Dhaka and port city of Chittagong, witnesses said, to guard against any escalation in violence.
In Dhaka, thousands of protesters had stayed out on the streets since late on Tuesday to vent their anger at the verdict handed to Mollah, 64, who was expected to be given a death sentence.
"Our protest will continue until the authorities put him to gallows," said Mohammad Zafar Iqbal, a university professor.
"The nation was taken by surprise when the court announced life imprisonment for war criminal Mollah. He must be hanged," said Nasiruddin Yusuf, a filmmaker and a 1971 war veteran.
The rally was centred on Dhaka's Shahabag Avenue, which protesters dubbed the "Tahrir Square of Bangladesh", recalling the scene of protests in Cairo which led to the overthrow of Egyptian strongman Hosni Mubarak.
Activists hanged an effigy of Mollah from an overhead iron bar, Reuters witnesses said.
Similar protest rallies were held on Wednesday in other major towns including Chittagong in the southeast and Sylhet in the northeast.
In an indication of the rifts opened up by the court, shops and businesses in the capital and elsewhere were shut as Jamaat-e-Islami enforced a national strike against the verdict.
Bangladesh became part of Pakistan at the end of British rule in 1947 but broke away in 1971 after a war between Bangladeshi nationalists, who were backed by India, and Pakistani forces that cost 3 million lives.
Some factions in what was then East Pakistan opposed the break with Pakistan, and numerous abuses were committed during the nine-month war. Jamaat denies accusations that it opposed independence and helped the Pakistani army.
The war crimes court handed down its first judgement last month, sentencing a former Jamaat leader and popular Islamic preacher Abul Kalam Azad to death for similar crimes. Azad was tried in absentia as he fled the country in April.
Eight other senior Jamaat leaders are on trial for war crimes, court officials said.
On Tuesday, Bangladeshi lawmakers criticised the court for delivering the "unexpected and muted judgement" on Mollah. Moinuddin Khan Badal from the National Socialist Party said the tribunal had "negotiated" its ethics and values.
Four people were killed and over 150 hurt, including 50 police, in Tuesday's Jamaat-led strike. Authorities later deployed troops in the capital Dhaka and Chittagong port city to help keep law and order.
Jamaat has threatened to paralyse the country unless Mollah and its other leaders on trial are freed and the tribunal dissolved.
Prime Minister Sheikh Hasina set up the tribunal in 2010 to investigate abuses during the 1971 conflict, but critics say she is using it as a political weapon against the two biggest opposition parties, the Bangladesh Nationalist Party and Jamaat-e-Islami.
The ruling Awami party has rejected accusations that the tribunal is biased but it has been criticised by human rights groups for failing to adhere to standards of international law.