Dhaka, Bangladesh (CNN) -- At least 37 people died in rioting across Bangladesh after the leader of the country's largest Islamist party was sentenced to death on decades-old allegations of war crimes.
Supporters of the Jamaat-e-Islami movement battled with police in several cities after 73-year-old Delwar Hossain Sayedee was sentenced to hang by a war crimes tribunal. The two-time member of parliament was convicted of eight of 20 counts involving killings and rapes during Bangladesh's war of independence in 1971.
During that war, between 1 million and 3 million people were killed, and hundreds of thousands of women were raped. In 2010, Bangladesh set up a court called the International Crimes Tribunal to finally bring to justice those it accused in the massacre.
Sayedee is the third of seven Jamaat party leaders to be charged with war crimes and the second to be sentenced to death.
Tens of thousands of people, including many of those who fought for the country more than 40 years ago, celebrated the judgment against Sayedee. But furious Jamaat supporters rioted in Dhaka and other cities after the decision, leaving at least four police officers among the dead, police and other officials said.
Police around the country fired gunshots and tear gas shells to disperse the mobs, who also exploded a series of homemade bombs.
Most of the people were killed in the districts of Rangpur, Gaibandha, Satkhira, Thakurgaon and Chittagong. At least two of the police officers were beaten to death in the streets, while a bomb killed a pedestrian in Dhaka, authorities said.
Monirul Islam, a Dhaka police spokesman, said two grenades were found near Shahbag Square, where thousands of people were celebrating the court verdict. The grenades, which were later defused, were found abandoned on the pavement near the five-star hotel Ruposhi Bangla, he said.
Home Affairs Minister Shamsul Haque told reporters that the government has stepped up security nationwide. Paramilitary troopers have been called in to patrol the troublesome cities, and the government has imposed ban on rallies and gatherings in some districts.
Since early February, widespread rallies have sprung in Dhaka's Shahbag intersection, with protesters calling for justice against war criminals and rejecting fundamentalism in politics.
But Jamaat has called the Shahbag participants "anti-Islamic atheists."
Increasingly, the Islamists are letting their presence known with larger and larger rallies and strikes first in cities outside Dhaka and then in the capital city. Violence has been reported with police firing shots and tear-gas to disperse mobs.
Jamaat-e-Islami called a nationwide general strike Thursday to protest the trial, which it called "politically motivated.
Physically separated by India, Bangladesh had been the eastern part of Pakistan until it gained independence in 1971 in a war. Jamaat-e-Islami opposed East Pakistan's struggle for independence and has decried what it calls a smear campaign against it.
CNN's Elizabeth Yuan contributed to this report.