The sentence Thursday for Delawar Hossain Sayeedi, a leader of the Jamaat-e-Islami party, reverberated across the country.
It was celebrated by people who condem Jamaat and call for justice in the war crimes cases and reviled by Jamaat supporters who said the charges against Sayeedi and others were politically motivated, The New York Times reported Friday.
Six police officers were among the people killed in the confrontations, authorities said.
To protest the verdict against Sayeedi, Jamaat leaders called Thursday for a nationwide strike that devolved into violence, with party followers clashing with police, the Times said.
Sayeedi, who denied all the charges against him and said he would appeal, was ordered hanged by a tribunal called to investigate crimes committed during the 1971 war of independence that led eastern Pakistan's secession and emergence as Bangladesh. He was found guilty of charges that included mass murder, torture and rape.
Sayeedi's lawyer, Abdur Razzaq, accused authorities of prejudicing the trial and of barring a key witness from testifying.
"This is unfortunate, and this is unexpected," Razzaq told the Times in a telephone interview. "This is a perverse judgment. It is inconceivable that a court of law awarded him a conviction. This prosecution was for a political purpose."
So far, the war crimes tribunal has convicted three Jamaat leaders in relation to the war.
Jamaat leaders and other opposition politicians have said the government was manipulating the process to take on political rivals, which authorities have denied.
Human rights groups have said the tribunal does not conform to international standards.