Opposition groups in Bangladesh have called for a countrywide strike on Sunday, following the execution of an opposition politician.
Abdul Quader Mollah, 65, was the first person to be put to death for massacres committed during the bloody 1971 war of independence.
The execution was expected to further inflame tensions in Bangladesh after weeks of deadly violence, and there were reports of fresh clashes soon after the announcement.
Finally after four decades, the victims of the genocides of 1971 liberation war have got some justice.
Mollah was a senior leader of the Jamaat-e-Islami party which has called the execution a "political murder" and warned of exacting revenge for "every drop" of his blood.
Deputy law minister Quamrul Islam announced the execution, saying Mollah was hanged by the neck on Friday in a jail in the capital, Dhaka.
"It's an historic moment. Finally after four decades, the victims of the genocides of 1971 liberation war have got some justice," Islam told the AFP news agency.
"It's the best gift for [the] nation as we celebrate the Victory Day on December 16," he said, referring to the national day that marked Bangladesh's independence war victory against Pakistan.
The government says Pakistani soldiers, aided by local collaborators, killed 3 million people and raped 200,000 women during the war.
While there was no immediate violence at the prison, local media and police reported that Islamists and opposition protesters armed with crude bombs and rocks clashed with police in several cities shortly after the execution.
Mollah's case has divided opinion in the impoverished South Asian nation of 160 million.
Thousands of secular protesters erupted in celebration as news of the execution came.They had been camping at Shahbagh square in Dhaka for days, shouting slogans including: "Hang Quader Mollah, hang war criminals".
Mollah was found guilty in February of having been a leader of a pro-Pakistan militia which fought against the country's independence and killed some of Bangladesh's top professors, doctors, writers and journalists.
He was convicted of rape, murder and mass murder, including the killing of more than 350 unarmed civilians.
Mollah was one of five Islamists and other politicians sentenced to death by a much-criticised war tribunal, which the opposition says is aimed at eradicating its leaders.
Mollah was assistant secretary general of the Jamaat-e-Islami party, which is barred from contesting elections but plays a key role in the opposition movement led by the Bangladesh Nationalist Party (BNP).
The sentences have triggered riots and plunged the country into its worst violence since independence.
About 231 people have been killed in street protests since January, when the verdicts were first handed down.
Critics of the tribunal say it has been used as a political tool by Prime Minister Sheikh Hasina, who is locked in a feud with BNP leader Begum Khaleda Zia, as a way of weakening the opposition as January 5 elections approach.